Despite a lack of prior military experience, he proved an energetic and capable soldier, and was one of the most powerful men in England when the First Civil War ended in 1646.

Based on his support for the Congregationalist radical, Samuel Eaton, and the reforms advocated by Sir Henry Vane the Younger in 1641, Brereton appears to have sympathised with those who rejected the concept of state-ordained religion.

[5] Appointed Deputy lieutenant for Cheshire, he was an unusually active Justice of the Peace, or JP, attending over 80% of sessions held between 1625 and 1641; in the same period, only one other person managed over 40%.

[5] Perhaps surprisingly, when Brereton visited Glastonbury in 1635 he made a point of taking "a special view" of the Holy Thorn, a notoriously papistical plant; he "brought away many branches and leaves, and left the first letters of my name thereon upon record".

[2] Along with a number of other regions, at the beginning of the war some prominent Cheshire notables attempted to remain neutral, and in December 1642 issued the Bunbury Agreement, which demanded an end to fighting in the area.

[11] Over the next few years, Brereton waged an aggressive and relentless campaign throughout the North Midlands, one of his key subordinates being Colonel Robert Venables, a long-time family connection and friend, who later served in Ireland.

Their activities forced the Royalists to divert resources from other areas, as Chester was essential for funnelling men and material from their supporters in Ireland and North Wales.

At Nantwich in January 1644, their combined force routed Byron, who lost over 1,500 men, most of his artillery, and baggage train and spent most of the next two years blockaded in Chester.

[13] At Malpas in August 1644, Brereton added to his reputation by routing Royalist cavalry under Marmaduke Langdale who had escaped from the defeat at Marston Moor.

[16] As a reward for his services, Parliament granted him possession of Eccleshall Castle, seat of the Bishop of Lichfield, and Croydon Palace, owned by the Archbishop of Canterbury.

After Pride's Purge in December 1648, he retained his seat in the Rump Parliament, and was appointed to the High Court of Justice for the trial of Charles I in January 1649, although he did not attend.

His body was originally conveyed to St Mary's Church, Cheadle, Cheshire for burial, but whilst the funeral cortège made its way northwards a horse stumbled crossing a river in spate and the coffin was temporarily lost.