"We managed to gather the necessary number of votes [in the parliament] for the impeachment," the lawmakers said as quoted by the NHK broadcaster.
They added that the president should set the date of the resignation by herself, but the most appropriate time for it was the end of April.
On Tuesday, Park said in a speech that she was ready to resign if the parliament worked out a safe power transition procedure.
On October 24, media reported that Choi Soon-sil, a friend and "shadow adviser" of the president, allegedly received drafts of speeches and presidential documents, which could contain confidential information, though she had never held a public post.
On November 20, the Seoul Central District Prosecutor's Office filed formal charges against Choi and two of Park's former aides and stated that Park was suspected of being an accomplice in the conspiracy. South Korea's main opposition Democratic Party (The Minjoo) has announced plans to seek vote on Park's impeachment in December.