Born in Valletta, Malta, the daughter of Major-General Sir Robert Lock, she began writing poetry in 1921. In 1941, her first published book of poems appeared, No Other Choice. Her second volume of poetry was Fall of Leaf, from 1943.

In the early 1930s, she was a student at the Old Vic. In 1933 she married Michael Forrester Wood, an army officer. She met Ralph Vaughan Williams in 1938, after she sent him a play which she had hoped he would set to music. The meeting led eventually to their collaboration on the choral work Epithalamion. She and Vaughan Williams began an affair whilst still married to their respective spouses. Michael Wood died in 1942 whilst on Army duty, of a heart attack. After his death, Ursula Wood continued her relationship with Vaughan Williams, with the acknowledgment of Vaughan Williams' wife Adeline. Ursula Wood became Ralph's literary advisor and personal assistant.

Adeline Vaughan Williams died in 1951 after a long illness. Ursula Wood and Ralph Vaughan Williams married in February 1953. She encouraged her husband to resume the composition he had been forced to set aside during his first wife's illness, writing the libretto to two of his last choral works, including the cantata for Christmas Hodie. Ralph Vaughan Williams died in 1958. Following her second husband's death, Ursula Vaughan Williams set up residence near Regent's Park, London.

In 1964 she published RVW: A Biography of Ralph Vaughan Williams. She completed her own autobiography, Paradise Remembered, in 1972, but did not publish the book until 2002. Additionally, she published four novels, including Set to Partners (1968) and The Yellow Dress (1984) , and five volumes of poetry. She provided libretti for other composers, including Herbert Howells, Malcolm Williamson and Elizabeth Lutyens, for example her famous "Hymn to St. Cecilia", which was put to music by Howells.

Until her death in London at age 96, she was honorary president of the Ralph Vaughan Williams Society. She was also the president of the English Folk Dance and Song Society.