The People's Association has confirmed that Ms Laura Ong, a constituency director of Pasir Ris West Constituency Office, has quit.
In a statement on Wednesday night, it said she tendered her resignation on Dec 10, citing family commitments.
"The People's Association has accepted her resignation," said the spokesman.
Ms Ong is understood to be the woman whom former Speaker of the House Michael Palmer had an extra-marital affair with.
Earlier on Wednesday, Mr Palmer announced his resignation as Speaker and MP for Punggol East.