His rise to importance was due primarily to his close friendship with Sir Thomas Wentworth, afterwards Earl of Strafford, who was his distant cousin.

Although at first hostile to Charles I, as shown by the active part he took in the impeachment of George Villiers, 1st Duke of Buckingham, Wandesford soon became a royalist partisan, and in 1633 he accompanied Wentworth to Ireland, where he became Master of the Rolls.

In 1640 Wandesford succeeded Strafford as Lord Deputy of Ireland, but he had only just begun to struggle with the problems of his new position when he died,[2] after a short illness which seems to have been a severe fever, on 3 December 1640.

[2] Wandesford's younger daughter Alice Thornton (1626–1707) is still remembered for her Autobiography, first published in 1875, which is a valuable source for her father's life and career.

Her elder sister Katherine (died 1645) married Sir Thomas Danby and had sixteen children, of whom ten survived infancy.

[7] Apparently he regretted this decision on his death bed and asked that half the rent for the entire area for the last 21 years be repaid to the O'Brennans.

Strafford's biographer, C. V. Wedgwood, describes Wandesford as shy, self-effacing, tolerant and charitable, a profound thinker, a fine lawyer and a man who was deeply concerned for social justice.