Born the son of Richard Boyle and Elizabeth Boyle, Boyle was educated at the University of Oxford. He started his military career as a volunteer in the service of the Duke of Ormonde at the Battle of the Boyne in July 1690 during the Williamite War in Ireland. He also fought, being wounded and becoming a prisoner of war, at the Battle of Landen in July 1693 during the Nine Years' War. He was commissioned as a junior officer in Ormonde's Troop of Horse Guards and cornet in the Army on 16 February 1694 and was promoted to cornet in his regiment and major in the Army in 1697. Boyle succeeded his paternal grandfather as 2nd Viscount Shannon in 1699. He became colonel of Prince George of Denmark's Regiment of Marines in February 1702 and commanded a brigade of grenadiers during the storming of Vigo in October 1702 during the War of the Spanish Succession. During this engagement the entire French fleet, under the command of the Marquis de Château-Renault, together with the Spanish galleons and transports under Manuel de Velasco, were either been captured or destroyed. For his good conduct at Vigo, Boyle was sent home to present the despatches, which reported on the destruction of the French fleet, to Queen Anne. She rewarded him with a gratuity of £1,000. However, in January 1703 he was accused of being involved in some scandalous activity at St James's Church, Piccadilly. Promoted to brigadier-general in 1704, Boyle took part in a successful raid on Barcelona in 1705; he was again sent home to present the despatches. Queen Anne rewarded him with another gratuity. Promoted to major-general in 1708, he became Joint Controller for Clothing the Army that year. He also entered the House of Commons in 1708 as Member of Parliament for Arundel. His brief membership of the Kit-Cat Club, which met at the Trumpet tavern in London, gave him useful access to ministers and other key influencers including the Earl of Scarborough who had nominated him as a candidate for his seat in Parliament. At this time he was said to have had "an openness and frankness in his conversation which are highly engaging". In Parliament he supported the Whigs and voted for the Foreign Protestants Naturalization Act 1708 which allowed Protestants fleeing from the continent to enter Great Britain. Promoted to lieutenant general in 1709, Boyle became Deputy Governor of Dover Castle later that year and was then given command of a secret but abortive expedition to attack New France in 1710. As the Earl of Scarborough was no longer in a position to nominate both members for Arundel, Boyle changed constituency to Hythe for which seat he was nominated by Lionel Sackville, 1st Duke of Dorset, in 1710. In Parliament, in accordance with Whig party policy, he voted for the impeachment of Henry Sacheverell, a clergyman who had criticised the party, in March 1710.