I FIRST ran across Giuseppe (Iseppo) da Porto and his son forty years ago, in Florence. When I next did so thirty years later, it was in Paris, in the Palais de Luxembourg, and I am pretty sure the boy was called Adriano.

It was not until the winter of 2006/07 that I met his wife, Contessa Livia Thiene, and their daughter, Porzia, who clung tenaciously to her mother's coat tails. The family owned a palatial home in Vicenza, but had long since moved out. They made it to Paris in 2009 (Arts, 13 November 2009), travelling more in the space of a decade than ever before.

The 2006 V&A show "At Home in Renaissance Italy" was only the second occasion that the family had been able to come together since the pair of portraits by Paolo Veronese were separated. They now stand, either side of a large domestic scene (The Supper at Emmaus), welcoming visitors to the latest sumptuous exhibition to open in Trafalgar Square as once they might have done in their Palladian villa.

The Da Porto-Thienes seemingly commissioned Veronese in 1551/52 for the double portraits as soon as they moved into their new home, where five more sons were born. The Mediterranean and the Atlantic now keep them apart: she is currently in Baltimore, while he has been in the Uffizi since 1970.

Dr Xavier Salomon, who has returned to the National Gallery to curate this exhibition of 50 of Veronese's paintings from Fifth Avenue, New York, has established that the children in fact had impossibly grand classical names (Leonida, poor chap, and Deidamia). It is quite likely that the portraits commemorate the move to their newly completed villa.

The full-length portraits, a feature of mainland northern Italian art, are imposing solely because of their size; they are observed humanely and with a degree of intimacy that suggests that the humbly born stonecutter's son felt at ease portraying the well-to-do. He is known to have painted about 40 portraits, and a further five are in this show, including the great Lascelles portrait of a member of the Saranzo family, hanging next to one still owned by the Prince Colonna.

Paolo Bazaro was born into a family of stonemasons originally from Lake Lugano; his father is credited with the hunchback water stoups in the church of Sant' Anastasia in Verona and hadworked with the architect Michele Sanmicheli at the Villa Saranzo at Castelfranco and presumably on the new city gates of Verona.

From 5 July to 5 October, Verona itself hosts a parallel exhibition, the first retrospective in Italy since the Fascist one in Venice in 1939. The National Gallery jointly secured the loan of 25 paintings for both shows; thereafter, both shows differ widely, not least as the Italians will see Veronese's all-important drawings for many of the pictures.

Veronese's mother was the illegitimate daughter of a minor landed family called Caliari (a name the young artist later took for himself) and stepdaughter of Leonardo Bevilacqua Lazise, whose cousins gave the 18-year-old artist one of his first commissions for an altarpiece around 1546.

This was for a mortuary chapel in the Church of San Fermo Maggiore in the city from which he so proudly took his name when he moved to Venice the following decade. That altarpiece has suffered badly, and was not worth showing, but the precocity of the youthful artist in his first painted sketch for it is evident.

What turned a stonecutter into a great painter is only hinted at in the first gallery, but across his 40-year career (he died at the comparatively early age of 60 in the year of the Spanish Armada), we get to see how his use of colour transformed mainland Veneto and the Maritime Republic of Venice.

Verona is rich in Roman antiquities but had become something of an artistic backwater for painters after the death of Andrea Mantegna in 1506. Good local stone, however, meant that it sustained a strong tradition of architecture and of stonemasonry. We get to see the pink-grained local marble in the 1562 altarpiece for the Bonaldi family (Accademia, Venice).

The artist never forgot his background training with his father and his uncle, and architectural members repeatedly appear in his paintings. One of the first painters with whom he trained as a teenager, Giovanni Battista Caroto, published a volume of the antiquities of Verona (1560). Dr Salomon points out that Veronese would have known his woodcut of a pilaster's acanthus scrolls from the cathedral.

This haunting detail is included in the steps of the bishop's throne in the Consecration of St Nicholas (1562) and those below the Virgin in the Mystic Marriage of Saint Catherine (Accademia, Venice). It recurs as late as in the Four Allegories of Love (National Gallery), here lovingly re-installed in the octagonal Room 11 where they always used to hang.

The solidity of his painted architecture should come as no surprise when we recall that perhaps Veronese's greatest artistic triumph came with his frescoes for the Villa Barbaro at Maser and for the ceilings of the Doge's Palace and churches such as San Sebastiano in Venice, aspects necessarily beyond the scope of this staging.

Yet architecture is always included artfully. The Virgin and Child enthroned in the Bevilacqua Lazise altarpiece sit comfortably on a stone daïs, while a balustraded arch sweeps across the background of The Raising of the Daughter of Jairus, a painted sketch for a long-lost altarpiece of the same year.

George Villiers, the ill-fated favourite of King James VI and I and boon companion of his son, later King Charles I, once owned the Anointing of David. As a painting about the succession of kings, it would have had a particular message for its Stuart owner.

Veronese stays close to the biblical text of 1 Samuel 16.1-13. David, Jesse's eighth son and the chosen one, kneels in front of a classical altar as Samuel pours oil into a horn with which to anoint him. The sacrificial cow, or at least half a heifer, since its back legs are clearly missing, muses on the fate that it has escaped. The family group is framed on either side by remarkable architectural references, as the past and the newly rebuilt classical cities of the mainland are celebrated.

Architecture similarly embraces The Supper at Emmaus, the earliest of Veronese's famed series of large-scale biblical feasts, and the only one to be included in the exhibition. In the crowded scene, there are nine children and a babe in arms to start with, and three brothers with the wife of one of them. The Risen Christ does not get a word in edgeways, but carries on blessing the bread in front of them, ignored by everyone except for one disciple.

But this is no out-of-town inn. The setting is the grand loggia of a villa with fluted columns and a pedimented doorway and a rich marble floor. The side buffet groans with silver gilt in an ostentatious display from which a negro serving man fetches a dish.

Within the self-imposed constraint of displaying paintings that are uniformly accepted as autograph works of the master, and not of his increasingly extensive workshop, Dr Salomon has included all ten of the host collection.

These include The Conversion of Mary Magdalene, which was acquired in 1876 as Christ and the Woman taken in Adultery, in which Christ points significantly to the ground. The current Director of the NG, in his magisterial catalogue of the 16th-century Italian paintings in the collection (2008), accepted a colleague's proposal that it depicted the healing of the woman with an issue of blood (Luke 8.43ff) in place of his own descriptive title of Christ and a Kneeling Woman. Neither of the central protagonists is older than the 20-year-old artist who brings them to us.

The first painting ever acquired by the would-be philanthropists who had in mind establishing a National Gallery as early as 1811 was The Consecration of St Nicholas. This is one of three altarpieces that Veronese painted in 1562 for the Benedictine abbey church ofSan Benedetto in Polirone, south of Mantua. Only two survive. It is joined here by the other from the Chrysler Museum of Art in Norfolk, Virginia, USA (The Virgin and Child Appear to St Anthony Abbot and Paul the Hermit).

Subtle minutiae emphasise the scholarship of this Benedictine community: surprised into being chosen as bishop, the pious Nicholas has set aside his prayer book, a paper marking the page, while the founder of monasticism has a book open on a rustic wooden reading bench beside him. The third picture is known only from a copy, and depicted St Jerome,the producer of the Vulgate Bible.

Such details were important to the artist and his patrons. In the Prado's Finding of Moses, we get to see the basket of bulrushes from which the baby has been saved by Pharaoh's daughter, while Miriam has already fetched their mother to act as the wet nurse. These two women are distinguished by the modesty of their dress from the princess's ladies-in-waiting to the left, who debate with a dwarf how to care for the Hebrew castaway.

The Rest on the Flight into Egypt is in the John and Mable Ringling Museum of Art, Florida, where it was central to an exhibition of Veronese and his contemporaries a year ago. Besides Matthew 2.14, the canvas explores the episode from the Gospel of Pseudo-Matthew (fifth century), in which the thirsty refugees shelter from the sun under a palm tree, a tradition known still in the Qur'an, and common to many African countries, where the date palm provides so richly for life.

Angels abound as one plucks the fruit from the bough, hanging perilously from its branch, while another catches the dates in a folded cloth. Joseph has found a water source, and the knife prominently laid on the swaddling clothes recalls the first shedding of Christ's blood at his circumcision. A loaf of bread in the foreground points to the eucharist. The trunk of the date palms form a cross, and a nail sticks out of the wooden stall behind the Virgin's head.

The nation also owns a version of the Rape of Europa (unsatisfactory as this small work appears, close up) and the Dream of the Empress Helena, brilliantly paired off here with a very different composition of the same scene from the Vatican, and the spectacular Family of Darius before Alexander (1565-67).

The scale of this picture, which is 4.75 metres long and whose height (2.36 metres) makes the horse Bucephalus appear all too real, makes it unlikely that Veronese painted it singlehandedly, but there are few weak passages in it. The arcade in the background is at one with his usual habit of including architecture at every turn, while the figures offer no doubt. Hephaiston and his friend Alexander are dignified young men in any age.

By staging the exhibition on the main gallery floor and for once not in the Stygian gloom of the Sainsbury Wing basement, the NG can show large canvases, and, much more importantly, enable them to be seen by natural light.

Three prestigious loans from churches, willingly and generously offered, stand out, both by their size and their quality. The Vicentine Church of Santa Corona has sent its version of the Adoration of the Magi (1573), which here faces the NG's own narrative version of the scene, painted around the same time for the Scuola di San Guiseppe at the Church of San Silvestro in Venice. The verticality of the altarpiece is emphasised by the cinematic way in which contrasts of light and colour enhance the biblical scene in which the oldest of the kings scrutinises the naked Christ-child.

The tallest altarpiece is arguably Veronese's finest work. Depicting St George in the moment when he accepts that the cost of rejecting the worship of a pagan divinity is death at the hands of an executioner, it was painted for the high altar of San Giorgio in Braida, overlooking the river Adige in Verona, around the time of Veronese's marriage (1566).

Sanmicheli had designed the altar (and redesigned the church), and Veronese provided a theatrical tour de force, in which the Roman soldier's pale skin is contrasted to that of the executioner and the page-boy in the background. Two mounted soldiers tower over the kneeling saint from either side, unaware that Faith has despatched a putto with palm branch and laurel crown to greet the new martyr.

The Conversion of St Pantalon, the last picture in the show, and a fitting conclusion, comes from its eponymous church in the heart of Venice. It was painted in 1587 for the old high altar, and the later reorientation of the church makes it impossible to see the picture properly in situ. I have tried, more than once, honest. Just to see it displayed is earthly reward indeed.

"Veronese Magnificence in Renaissance Venice" is at the National Gallery, Trafalgar Square, London WC2, until 15 June. Phone 020 7747 2885.
www.nationalgallery.org.uk