Thumboo Chetty was born in April 1837 to a Catholic family, apparently in Trichinopoly,[citation needed] to Desayi Royalu Chetty Garu, a chief bookkeeper in Griffith's and Co., in a mercantile firm, and Catherine Ummah, a woman of piety, mildness, courtesy and serenity.

Thumboo Chetty's forebear, Gowri Koolapathi Kampal Naidu from Kottapalayam, originally practiced Hinduism.

Kampal Naidu marked the initiation of Catholicism within the family when he converted to the Catholic faith through the efforts of Saint Francis Xavier in 1545.

This historical event is documented in the initial Baptism Register of the Kottapalayam Church at Mettur in Salem District.

Thumboo Chetty married Rajamma, daughter of Ponnoo Chettiar and Sinnammalle, Church of the Blessed Virgin Mary of Refuge, Pophan’s Broadway, Madras.