Raimondi was born in Milan, Italy. He was the younger brother of Antonio Raimondi, a prominent naturalist who worked in Peru. Timoleon was ordained as a priest on 25 May 1850. He was appointed as prefect of Hong Kong in Hong Kong on 27 December 1868.
Raimondi was also:
Titular Bishop of Achantus and Hong Kong – 4 October 1874