Joining the Indian Civil Service in 1922, Pillai initially served in the Central Provinces as an assistant commissioner and as an officiating deputy commissioner from March–November 1927. During his career with the ICS, Pillai was appointed to various secretarial positions in the then United Provinces. He successively served as an assistant collector of customs at Chennai (December 1927 – May 1929) and as deputy director of commercial intelligence at Kolkata (May 1929 – March 1932). He was promoted to deputy secretary in March 1932, joining the Commerce Department. He was advanced to temporary joint secretary (June 1934) and to joint secretary (officiating) in February 1936, being appointed collector at Karachi in April 1936. From April 1937, he was an officer on special duty with the Commerce Department, and was appointed as a deputy commissioner in July. He was promoted to joint secretary in the Commerce Department in April 1938, to additional secretary in February 1941 and finally to full secretary in October 1942.