This first by-election in 20 years was held to fill the vacated seat of Hougang after its new WP Member of Parliament Yaw Shin Leong, who succeeded the ward from WP secretary-general and previous incumbent Low Thia Khiang last year, was expelled from the party for failing to clarify allegations surrounding his personal indiscretions.

Rumours first surfaced online at the start of the year. In early February, Yaw resigned from WP's executive council, where he held the post of treasurer, with no explanation. This failed to appease Low and the party leadership, which voted in favour of the expulsion. According to Singapore's laws, a MP loses his seat if he is no longer member of the party that he was elected under. Having relocated overseas and declining to appeal against WP's decision, Yaw's four-month tenure as a legislator officially ended on 14 February 2012 and was the shortest ever in Singapore history.

Despite being non-committal to a by-election earlier, Prime Minister Lee Hsien Loong advised President Tony Tan to issue a writ. At the same time, he criticised WP for letting voters down. Earlier on 2 March 2012, an Hougang resident filed an affidavit for mandatory by-elections within three months or reasonable time as decided by the courts, rather than to allow the PM unfettered discretion in holding one.

A WP candidate of East Coast GRC in last year's election was fielded in Yaw's place and faced the same PAP candidate, who had remained grassroots leader of the ward. Other opposition parties announced that they would stay out of the fray. Dr Poh Lee Guan and Zeng Guoyuan, both past WP candidates of the 2011 and 1991 GEs respectively, applied for and were issued political donation certificates but neither contested. Dr Poh, still a WP member then, was also expelled after the by-election for his unilateral decision to be WP's "back-up candidate".

During the campaign, Deputy PM Teo Chee Hean questioned Png Eng Huat's honesty over his statements on rejecting the Non-Constituency MP seat, while Low and WP leaders took issue with Desmond Choo's "independent" claim.

For the first time in Singapore's history, the required election deposit sum decreased, after the salary cut of ministers and MPs earlier in the year. With a nearly 30% advantage the last time, WP won comfortably with its margin slightly reduced.

Writ of election:
  9 May 2012, Wednesday
Nomination day:
  16 May 2012, Wednesday
Cooling-off day:
  25 May 2012, Friday
Polling day:
  26 May 2012, Saturday
Overseas vote-counting:
  30 May 2012, Wednesday
Member swearing-in:
  9 July 2012, Monday

Eligible voters:
  23,368 [OV: 43]
Voter turnout:
  21,978 [OV: 27] (94.1%)
Election deposit:
  $13,500 (-$2,500)

Workers' Party 13,460 (62.1%)
[OV: 13]
People's Action Party 8,223 (37.9%)
[OV: 13]
PNG Eng Huat
50  |  M  |  Businessman
Desmond CHOO Pey Ching
34  |  M  |  Union deputy director
Workers' Party wins by margin of 5,237 (24.2%)
Valid votes: 21,683 (98.7%)
[OV: 26]
Rejected votes: 295 (1.3%)
[OV: 1]
Previous election > GE 2011 > Workers' Party won 64.8% > Swing -2.7%

Party Current MPs Candidates Won New MPs
People's Action Party 81 1 0 81
Workers' Party 5 1 1 6
Previous seats > GE 2011