Bastwick was a Puritan and he was imprisoned several times for his controversial writings. Bastwick became friendly with John Lilburne who helped him get his books and pamphlets published in Holland.
Bastwick was released from prison in 1640 and during the Civil War served in the Parliamentary army. After the war Bastwick, a Presbyterian, advocated the persecution of other Puritan groups such as the Anabaptists, Quakers and Congregationalists. When his old friend, John Lilburne, complained, Bastwick arranged for him to be arrested.