K Muralidharan Pillai, 48, was introduced by Deputy Prime Minister Tharman Shanmugaratnam as the PAP's candidate for Bukit Batok constituency at a press conference here.
Pillai has served as secretary of the PAP's branch in the constituency from 2007 to 2011. He held roles such as the chairman of the ward's Inter-Racial and Religious Confidence Circle and vice-chairman of its community foundation.
53-year-old Chee Soon Juan, one of the most vociferous opposition politician and Secretary-General of Singapore Democratic Party, has also announced to contest the bypoll.
The volunteer has resigned from the PAP, which has ruled Singapore for over five decades since independence in 1965.
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The byelection is set to test PAP's popularity after it swept through absolute majority in parliament in the general election last September.
The party took 83 of the 89 seats, riding on a wave of patriotism inspired by last year's 50th anniversary of independence and respect for the country's independence leader, former premier Lee Kuan Yew, who died in March 2015.