"I would like to propose to the people that we should now quickly pursue constitutional revision," Woo Won-shik, the National Assembly speaker, told a press conference on Sunday.
"After going through the unconstitutional and illegal martial law and (then Yoon's) impeachment, the public consensus on the urgency of constitutional revision is greater than ever."
He proposed a national referendum on constitutional reform to coincide with the presidential election that must be held within two months of Yoon's ouster on Friday by the nation's Constitutional Court.
The court upheld parliament's impeachment of Yoon for briefly declaring martial law on December 3, sparking South Korea's worst political crisis in decades.
"The national confusion has come to an end with the Constitutional Court's ruling, but the potential for destructive conflict surrounding presidential power still exists," said Woo, adding that many South Koreans want to change the "imperial presidency", which he called a source of extreme political conflict.
A Gallup Korea opinion survey last month found 54% supporting constitutional revision to fix the presidential system and 30% saying that is unnecessary.
Yoon said on Sunday that although he had stepped down, he would "always stand by" his supporters, who fought for "freedom and defending sovereignty".
Acting President Han Duck-soo and the election commission are considering June 3 for the election date, the commission has said.
The constitution was last revised in 1987 to introduce direct presidential elections and a single, five-year term.
In recent years, presidential candidates from across the political spectrum have supported revisions, including giving presidents two four-year terms.'
However, there have been few concrete steps since new leaders were chosen.
Yoon's ruling People Power Party is studying possible amendments, and its presidential hopefuls have mentioned barring presidents from seeking more than two four-year terms.
The leading candidate to replace Yoon, main opposition Democratic Party leader Lee Jae-myung, has also discussed the idea.
