He attended Christ Church, Oxford. By 1640 he had become a captain in the army raised for Thomas Wentworth, 1st Earl of Strafford and in the same year was elected M.P. for Tyrone. In 1641 he led the attack on Strafford in the Irish House of Commons, presenting articles of impeachment against Sir Richard Bolton, Lord Chancellor of Ireland; John Bramhall, Bishop of Derry; Sir Gerard Lowther, Chief Justice of the Irish Common Pleas; and Sir George Radcliffe, member of the Privy Council of Ireland. These were friends and ministers of the Earl of Strafford, then under impeachment by the Commons of England.
Between 1641 and 1661 he served in the Army, rising to the rank of Colonel. At one point he was arrested and returned to England but was shortly thereafter allowed to go back to Ulster. In 1660 he was appointed as one of twelve commissioners sent from Tyrone to Charles II, was knighted, and was appointed to the post of prime serjeant-at-law, the senior law post in Ireland. James Butler, 2nd Duke of Ormonde, however distrusted him and preferred to take advice only from the Attorney General for Ireland, Sir William Domville, so that in a few years Mervyn's role as legal adviser effectively lapsed.
He was chosen Speaker in the House of Commons in May 1661 when again member for Tyrone, rather against the wishes of the King, who wanted William Domville. Shortly thereafter he went to England for nine months between September 1661 and May 1662 to take part in negotiations on the Act of Settlement 1662. When he returned he played an influential role in the House and was at the same time involved in a court set up to adjudicate land claims. This led to charges of corruption against him. He was speaker until the dissolution of Parliament in 1666.
According to the Oxford Dictionary of National Biography, "Opinions concerning Mervyn, both in his own day and since, have been various, but rarely complimentary, with frequent accusations of corruption, lack of scruple, or the pursuit of self-interest above principle."
- Burke, John (1835). A Genealogical and Heraldic History of the Commoners of Great Britain and Ireland, Enjoying Territorial Possessions Or High Official Rank, But Uninvested with Heritable Honours.|page=109|url=http://books.google.co.uk/books?id=0I9AAAAAcAAJ&pg=PA109&dq="Audley+Mervyn"+Tyrone+speaker+house+of+commons&hl=en&ei=lJTyS5WzMIKUnwOJr52wDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCwQ6AEwAA#v=onepage&q=%22Audley%20Mervyn%22%20Tyrone%20speaker%20house%20of%20commons&f=false
- R. M. Armstrong, ‘Mervyn , Sir Audley (1603?–1675)’, Oxford Dictionary of National Biography, Oxford University Press, Sept 2004; online edn, Oct 2006 accessed 18 May 2010