The WP said in a statement on Wednesday that it had it would not be nominating another party MP to the post.
It said the position of Leader of the Opposition in Singapore is a discretionary appointment that the prime minister makes.
"To this end, it is important to reiterate that the LO appointment in parliament arose out of the political success of the opposition at the ballot box.
In other Westminster systems, the title of the Leader of the Opposition is established by law and is not the prerogative or choice of the government of the day or the prime minister. This approach expresses the authority and sanctity of the people’s vote," it added.
"As such, the Workers’ Party has conveyed to the prime minister that we will not be nominating another Workers’ Party Member of Parliament to the LO post," the party said.
"We continue to focus on our primary duty, to work for Singaporeans and provide a rational, responsible, and respectable check on the government.”