Singapore's parliament speaker Michael Palmer announced his resignation on Wednesday over an extramarital affair with a staff member of the People's Association, a statutory body leading efforts to reach out to members of the public.

"I have resigned to take full responsibility for a grave mistake that I have committed," Palmer said in a statement. "My conduct was improper and it was a serious error of judgement. I have resigned in order to avoid further embarrassment to the People's Action Party and to parliament."

Prime Minister Lee Hsien Loong, secretary-general of the ruling People's Action Party, was informed and accepted the resignation of Palmer.

Lee will nominate a new speaker of parliament when it meets the next time, said Deputy Prime Minister Teo Chee Hean, who is also the first assistant secretary-general of the People's Action Party.

The prime minister will decide whether there will be a by- election, he added.

The person who had a relationship with Palmer did not work together with him directly, but worked in the Pasir Ris-Punggol group representation constituency where Palmer was a lawmaker.

Palmer told a press conference on Wednesday that he was deeply sorry for letting down his residents, the ruling People's Action Party and everyone who has believed and supported him.

"I apologize unreservedly to them and to my family. May I humbly request you be kind enough to respect my family's privacy during this very difficult time," he said.

Teo said Palmer had personally informed him about the matter and of his intention to resign. He said he agreed that Palmer should resign.

Singapore's ruling party has been sticking to very rigid standards in terms of the personal life of its members over the past decades.

A lawyer by training, Palmer took office as speaker of the parliament in October 2011. He was the youngest speaker of parliament. He is married with one child.

Arrangements had been made over the last two days to ensure that the transition is done properly, Teo said.