He was father of the Dutch novelist Maarten Maartens, the pen-name of Jozua Schwartz.
Carl Schwartz converted to Christianity while at University. Schwartz was minister of Trinity Chapel, in Newnham Street (earlier John Street) off the Edgware Road. There he succeeded the previous minister, Ridley Herschell. Schwartz in 1865 sent letters to many Christians of Jewish origin known to him, calling for a united Hebrew Christian congregation.
- The Free Church of Scotland monthly record - Page 684 1863 "The Rev. Dr. Schwartz, our late missionary to the Jews in Amsterdam, has now been formally appointed agent in London for the Free Church Mission to the Jews. He is now minister of Trinity Chapel, Newnham Street, Edgware Road."
- "The inheritance of J.M.W. van der Poorten Schwartz was partly Jewish, which may account in a measure for the passionate intensity of his beliefs. His father, Dr Carl Schwartz, was born in Germany of Hebrew parents, but, during his university days, he became a Christian. Though it had been his intention to devote himself to an academic career, he grew to realise the spiritual needs of his own race, and he gave up every other prospect in life in order to be an evangelist to the Jews." (Norreys Jephson O'Conor, 'A Memoir', in: Ada van der Poorten Schwartz (ed.), The Letters of Maarten Maartens, Constable & Co., London, 1930, Page xxviii)
- Dan Cohn-Sherbok, The image of the Judaeo-Christians in ancient Jewish and Christian ... ed. Peter J. Tomson, Doris Lambers-Petry, 2003, Page 287 "In 1865 an attempt was made by Dr. C. Schwartz, minister of Trinity Chapel, Edgware Road, London to unite all Jewish Christians" (reprinted/revised from chapter in Messianic Judaism 2000, Page 16)