Robert returned to Scotland about 1638, and took part in some of the early incidents of the Bishops Wars against Charles I and also in the Wars of the Three Kingdoms in service of the Scottish Covenanters. During the Bishops' Wars, in 1638 Dalkeith was won by Monro with 500 men, and in 1639 Monro was with Alexander Leslie when he captured Edinburgh Castle. General Robert Monro laid siege to the fortified Spynie Palace forcing Bishop John Guthrie to surrender to his forces.
Robert returned to Scotland around 1638, engaging in some of the early battles of the Bishops' Wars against Charles I and also participating in the conflicts of the Three Kingdoms War on behalf of the Scottish Covenanters. Monro's forces captured Dalkeith in 1638, and he later joined Leslie when they took Edinburgh Castle in 1639. General Robert Monro laid siege to Spynie Palace, forcing Bishop John Guthrie to surrender to his army.