He then worked for a time with Sir John Vanbrugh, helping him build Blenheim Palace for John Churchill, 1st Duke of Marlborough, where he took charge after Vanbrugh's final break with the demanding Duchess of Marlborough, and Castle Howard for Charles Howard, later the 3rd Earl of Carlisle. There is no doubt that Hawksmoor brought to the brilliant amateur the professional grounding he had received from Wren, and in Colvin's words, "enabled Vanbrugh's heroic designs to be translated into actuality."

Hawksmoor conceived the idea of a round library for the Radcliffe Camera but did not design that building himself. He did design the Clarendon Building at Oxford, All Souls College, Oxford, and six new churches in London. He also designed the west front of Westminster Abbey and became Surveyor of the Abbey when Wren died in 1723.

Unlike many of his contemporaries, Hawksmoor never travelled to Italy where he might have been influenced by the style of architecture there. He got his ideas from engravings books that went back to the purer Greek and Roman styles, but he was versatile in his work, and all the buildings he designed are distinctly different from each other.

Hawksmoor's six London churches

These churches were built in accordance with a Parliamentary act of 1711 providing tax money for the building of fifty new London churches. These six churches are Hawksmoor's best-known wholly independent works of architecture. They compare in their complexity of interpenetrating internal spaces with current work in Italy by Francesco Borromini. Their spires, essentially Gothic outlines executed in innovative and imaginative Classical detail, dominated the London skyline as a counterpoint to St. Paul's dome, deep into the 20th century.

• St Alfege's Church, Greenwich
• St George's Bloomsbury
• Christ Church, Spitalfields
• St George in the East, Wapping
• St Mary Woolnoth
• St Anne, Limehouse