Tan was born into a family of tailors. He was admitted to a premier school in Guangzhou in 1905. Upon graduation, he joined the budding Tongmenghui under the influence of Sun Yat-sen. He enrolled into Peking University's philosophy faculty in 1917 whilst participating in the May Fourth Movement. As a protest to the 21 demands he was part of the group of students who surged and set fire to the house of Minister of TransportCao Rulin, subsequently being arrested for his actions.
In 1920 Tan went back to Guangdong to form a Marxist group. He was appointed as the Secretary of the CPC Guangdong branch upon the founding of the Communist Party of China in 1921. He participated the 3rd National Congress of the Communist Party of China and was elected into the Central Committee. In the 4th and 5th Congress of the CPC, he was reappointed as a member of the Central Committee and also held membership in the CPC Central Committee Political Bureau. In August 1927 he was one of the leaders that started the Nanchang Rebellion against the Nationalist Government led by Jiang Jieshi. During the course of the rebellion, he recruited He Long into the CPC. Tan went back to Shanghai after the failure of the rebellion. In an enlarged meeting of the Politburo in November, Zhang Guotao appealed to the Comintern for the removal of Tan from the party as he blamed the failure of the Nanchang Uprising due to his leftist-tendencies. Losing his CPC membership, he sought after Deng Yanda for assistance in setting up an alternative Marxist enclave but was to no avail.
Membership in the Kuomintang
Tan participated in the 1st National Congress of the Kuomintang in 1924 and was elected into the Standing Central Committee and appointed as a Minister in the Central Organization Department of Kuomintang. In March 1937 he was appointed as a member of the Wuhan National Government and retained his post as the Minister for Agriculture. At the outbreak of the Second Sino-Japanese War, Tan returned to Wuhan seeking to help the Nationalist Party. Warmly received by Jiang Jieshi, he restored his dormant membership in the KMT and was soon elected into the 1st to 4th National Political Council. In January 1948, he was in Hong Kong to participate in the founding of the Revolutionary Committee of the Chinese Kuomintang and served in the Central Standing Committee.