At age 13, he came back to Malaya from China and studied in Anglo-Chinese School Ipoh and St Xavier's Institution, Penang.

[2][3] In 1932, Leong returned to China and served the Chinese government as counsellor of the Ministry of Railways, legal adviser to the Executive Yuan, members of Overseas Chinese Affairs Commission, adviser to the Treaty Commission of the Ministry of Foreign Affairs and inspector of China consulates in the Philippines, Dutch East Indies, Malaya and South Africa from 1935.

[4] After the war ended and subsequent Japanese surrender, a negotiation was held between him and the British Malayan authorities where he agreed for the OCAJA under his authority being absorbed into the national Special Constabulary in 1947 to fight alongside the British against the Communist-influenced Malayan National Liberation Army (MNLA).

[4] On 27 February 1949, Tan Cheng Lock founded the Malayan Chinese Association (MCA) along with Leong and Colonel H. S. Lee.

In 1958, he was awarded a federal title of Tun, bestowed by DYMM Seri Paduka Baginda Yang di-Pertuan Agong of Malaya.