His first electoral victory was a 1965 by-election for the
Rahang state legislative assembly seat in
Negeri Sembilan as an
independent using the symbol of a cherry blossom. The
Democratic Action Party (DAP) was still in the process of creation at the time, and was only registered on 18 March, following which Chen became its inaugural chairman. Chen Man Hin was one of the founders of the party in Seremban with other leaders such as
Lim Kit Siang,
Tan Seng Giaw,
Karpal Singh and Hu Sepang. The party headquarters was then located at Choo Teik Building, Seremban. In the 1980s, Negeri Sembilan was a stronghold of the DAP. He won his first federal parliamentary seat in
Seremban Timor, Negeri Sembilan in 1969 as a member of the DAP against
Barisan Nasional (BN). He subsequently won the elections of 1978 and 1986. In 1986, DAP won 24 parliamentary seats and 56 state seats. In the
1999 general elections, he lost in
Rasah, Negeri Sembilan to Goh Siow Huat from
Barisan Nasional. The party performed below expectations that year and the results were called "catastrophic" by Lim Kit Siang. Chen eventually resigned as Chairman of DAP and was replaced by Lim. ==Death==