LONDON.- The National Portrait Gallery has bought Sir Thomas Lawrence's outstanding but rarely-seen portrait of the leading 18th and early 19th-century actor and theatre manager John Philip Kemble. The painting, which hung in the artist's home until his death, will be included in the Gallery's major exhibition of Lawrence's work announced today and opening in autumn 2010.

John Philip Kemble as Cato has been acquired for a net price of £178,500 after tax concessions by Private Treaty Sale through Joseph Friedman Ltd acting on behalf of Mr John Philips of The Heath House, Staffordshire. It was purchased with help from Gift Aid Visitor ticket donations, Gallery supporters and a grant of £55,000 from The Art Fund, the UK's largest independent art charity.

At over eight feet tall and five feet wide, this monumental oil painting shows Kemble at the height of his career in the leading role of Joseph Addison's 1713 play Cato, in its 1811 revival. The portrait, which is little known by the British public having remained in a private collection apart from a single loan in 1983, is now expected to become one of the highlights of the Gallery's Regency Collection.

This is one of Lawrence's most outstanding portraits and one of the finest of a group of four experimental works in a new genre that Lawrence developed, which he called the 'half-history picture'. Painted a decade after the first three 'half-history' portraits, Kemble as Cato (1812) was the only one of the group to be commissioned and - the product of Lawrence's maturity of style and technique - was declared by the artist to be his best portrait of Kemble.

A tightly controlled and intensely philosophical portrait, Kemble as Cato focuses on the moment when Cato, unable to repel Caesar's forces, performs a soliloquy related to Plato's Book on the Immortality of the Soul. The glinting dagger on the table reminds us that he is preparing to take his own life to preserve his dignity in the face of defeat.

Just as Cato was defending Rome against invasion by Caesar so this scene had particular resonance for contemporary English audiences who, faced with the threat of Napoleonic invasion, saw Kemble in the role of Cato as a figure of resistance against foreign invaders and as a powerful symbol of national identity, individual liberties and patriotism.

When exhibited in 1812, the picture was widely admired, being praised not only for its likeness of Kemble but as a work that transcended the limits of portraiture and 'belonged to the highest school of history'. Lawrence was also pleased with the painting and when it was returned to him to make a reduced copy, for the actor Charles Mathews, the artist never returned it to its owner - the 1st Earl of Blessington. Instead, he used it as an advertisement of his talent by hanging it prominently at his fashionable new house in Russell Square. He wrote to the artist Joseph Farington: 'my front room is my show room, over the chimney of which is already placed my Cato'. This is where the painting remained until Lawrence's death in 1830, at which time the Earl of Blessington's executors had to apply to Lawrence's estate for its return.

The painting will join one of the world's finest and most accessible collections of Lawrence's paintings and will provide the Gallery with its only portrait of Kemble at the height of his career as an actor, manager and public figure.

John Philip Kemble was the leading actor and theatre manager of his day while Thomas Lawrence was the leading portrait painter of Regency Britain and the only British portraitist to have an international reputation at that time.

Dr Lucy Peltz, 18th Century Curator at the National Portrait Gallery, London, says: 'I'm delighted that the Gallery has been able to acquire Lawrence's magnificent portrait of John Philip Kemble as Cato. As the finest and most resolved of Lawrence's "half-history" portraits, the work will enrich the Gallery's capacity to explore the crucial dialogue between history painting and portraiture in the period, and will thus allow the Gallery to present a richer and more balanced account of the development of portraiture in the early 19th century.'