Marriott quit his job in 1798. He returned to Twinstead Hall and stayed there until he died on 21 March 1803, having rebuilt the local church. The year before he died he wrote his most important book, "Formulare instrumentarum", a book about his job with Naval law that caused Naval law in the United States to change. He also made a lot of poems and legal books that were not important. He never married, his one try in 1760 causing both the girl and her father to say "no." Instead he took care of his mother until her death.