 Alexander subscribed the Solemn League and Covenant at Aberdeen in 1638 and was a member of the General Assembly of the Church of Scotland at Glasgow in 1639.Also in 1639, while serving under the Earl of Montrose, he led 200 men against the castles of Kellie and Gight.He was chosen as a commissioner for Aberdeenshire in 1643 and this capacity attended the Convention of Estates in Edinburgh.