Born at Dinton Hall near Aylesbury in Buckinghamshire, Simon Mayne inherited the estate of his parents upon the death of his mother in January 1629. He attended the Inner Temple and married Jane Burgoine in 1633. After her death, he married Elizabeth Tow, a widow, with whom he had three sons. Mayne was active in the parliamentary committee for Buckinghamshire during the First Civil War, and acquired sequestered lands formerly belonging to the Church. He was elected recruiter MP for Aylesbury in September 1645.
In 1649, Mayne was appointed to the High Court of Justice and sat as one of the King's judges. He was a signatory of the death warrant.
Mayne surrendered at the Restoration, and was brought to trial as a regicide in October 1660. He was found guilty and sentenced to death. His wife Elizabeth engaged the lawyer Bulstrode Whitelocke to prepare an appeal to the King, but Mayne died a prisoner in the Tower of London in April 1661.
References:
W. P. Courtney, revised by Ruth Spalding, Simon Mayne , Oxford DNB, 2004