Richard Grenville, who later became Earl Temple, succeeded his uncle in 1749. When his mother died in 1752, he was widely acknowledged as the richest man in England. Much of the money went on refining the garden and giving the house its magnificent fronts.

Lancelot 'Capability' Brown was replaced by Richard Woodwood and Grenville began making changes - introducing sheep, to the consternation of his family, removing straight edges from lakes and canals and felling avenues of 'unnecessary' trees. He altered garden buildings, modifying the Grecian Temple (now the Temple of Concord and Victory), the Rotondo and the Boycott Pavilions among others, and overhauled the garden inside the Ha-Ha. He also sought to publicise his work, allowing a free market in guidebooks of Stowe.

Throughout the 1760s and 1770s he worked in bursts to alter or move the garden buildings, rather than building new ones. He also loved to entertain, using the Grotto for candlelit suppers with music and illuminations despite the cold, damp and distance from the kitchens.

In 1771, Earl Temple began his last great works, the building of both grand fronts. Planned by Robert Adam, reworked by Thomas Pitt and driven to completion by Earl Temple himself, the north and south fronts took eight years. By 1775 he had to be "wheeled among his workmen" as his health began to fail. He outlived the completion of the work by only five months. His death was grimly ironic - thrown from a chaise onto a heap of bricks, while driving at Stowe.