Charles Gerard was educated abroad, and in the Low Countries learnt soldiering, in which he showed himself proficient when on the outbreak of the Civil War in England he raised a troop of horse for the king's service. Gerard commanded a brigade with distinction at Edgehill, and gained further honors at the first battle of Newbury and at Newark in 1644, for which service he was appointed to the chief command in South Wales.
Here his operations in 1644 and 1645 were completely successful in reducing the Parliamentarians to subjection; but the severity with which he ravaged the country made him personally so unpopular that when, after the defeat at Naseby in June 1645, the king endeavoured to raise fresh forces in Wales, he was compelled to remove Gerard from the local command. Gerard was, however, retained in command of the king's guard during Charles' march from Wales to Oxford, and thence to Hereford and Chester in August 1645; and having been severely wounded at Rowton Heath on September 23, he reached Newark with Charles on October 4.
On November 8, 1645 he was created Baron Gerard, of Brandon in the County of Suffolk; but about the same time he appears to have forfeited Charles's favour by having attached himself to the party of Prince Rupert of the Rhine, with whom after the surrender of Oxford Gerard probably went abroad. He remained on the Continent throughout the whole period of the Commonwealth, sometimes in personal attendance on Charles II, at others serving in the wars under Turenne, and constantly engaged in plots and intrigues. For one of these, an alleged design on the life of Cromwell, his cousin Colonel John Gerard, was executed in the Tower in July 1654.
At the Restoration, Gerard rode at the head of the king's life-guards in his triumphal entry into London; his forfeited estates were restored, and he received lucrative offices and pensions. In 1668 he retired from the command of the king's guard to make room for the Duke of Monmouth, receiving, according to Pepys, the sum of £12,000 as solatium. On July 23, 1679 Gerard was created Earl of Macclesfield and Viscount Brandon. A few months later he entered into relations with Monmouth, and co-operated with Shaftesbury in protesting against the rejection of the Exclusion Bill.
In September 1685, a proclamation having been issued for his arrest, Macclesfield escaped abroad, and was outlawed. He returned with William of Orange in 1688, and commanded his body-guard in the march from Devonshire to London. By William he was made a privy councillor, and Lord Lieutenant of Wales and three western counties. Macclesfield died on January 7, 1694. By his French wife he left two sons and two daughters.