He became an attorney in London and was receiver-general for Hampshire, Wiltshire, and Gloucestershire from 1638 to 1649 on a life patent in succession to John Pym.
He became secretary to the Earl of Northumberland in 1639 and learned the basics of military administration during the Bishops' Wars.
Unlike his brother William Scawen he supported to the Parliamentary cause in the Civil War in adherence to the Earl of Northumberland.
In March 1660 he was commissioner for militia for Buckinghamshire and in May 1660 he resumed his post as Receiver-general for Hampshire, Wiltshire, and Gloucestershire.
[2] On 3 March 1662, Scawen was elected MP for Cockermouth in the Cavalier Parliament and in 1663 became a member of the Society of Mineral and Battery Works.