Upon completion of his studies, Boon Mark was employed by the American Presbyterian Mission in Siam as an evangelist in Phitsanulok province.

In April 1934, at the first General Assembly of the newly formed Church of Christ in Thailand [CCT], Boon Mark was elected as assistant secretary.

The Church of Christ in Thailand elected Boon Mark as general secretary in 1938, a position which he held until after World War II.

Boon Mark traveled widely throughout Thailand at this time, encouraging members of the CCT to endure the difficulties that they were facing.

Boon Mark played an important role in the 1956 Bangkok crusade meetings of American Pentecostal healing evangelist T.L.