Finance Minister Choi Sang-mok became on Friday South Korea’s second acting president in two weeks, as lawmakers voted to impeach the current acting leader, Prime Minister Han Duck-soo, fuelling political uncertainty in Asia's fourth-largest economy.

Han was replaced amid disagreements with the opposition on appointing justices to the Constitutional Court, which started deliberating an impeachment trial of President Yoon Suk Yeol after the opposition-led parliament impeached him on December 14 for his short-lived declaration of martial law on December 3.

Choi, 61, a veteran economic technocrat who has served for more than 30 years at the finance ministry, takes on an unprecedented role as successor to an impeached acting leader.

Before succeeding to the position, Choi said on Friday that impeaching Han would seriously damage the country's economic credibility and asked political parties to withdraw the plan.

Minutes after Han was impeached by parliament, Choi vowed “an all-out effort to stabilise state affairs” and overcome the current crisis, in the text of a speech issued by the ministry.

The South Korean won weakened to its lowest since March 2009, as analysts said there was little to reverse the negative sentiment stemming from the political uncertainty.

Choi has already been leading an unofficial gathering of financial authorities, known as F4, seeking to placate fears among international investors and allies over the political turmoil.

He has pledged “unlimited liquidity” to calm financial markets, spoken with U.S. Treasury Secretary Janet Yellen to reaffirm strong ties with South Korea's biggest ally, and sent letters of reassurance to finance chiefs of major nations.

Until recently, Choi was one of Yoon’s conservative loyalists in the cabinet, taking multiple roles since the president was elected in March 2022, starting as a secretary of the economy division.

He advanced to chief economic secretary, a position that allowed him to travel round the world with Yoon, before becoming finance minister in December 2023.

“Choi is more trusted by the opposition party lawmakers than Han Duck-soo, as someone who openly opposed Yoon’s martial law plan,” said a former minister who sought anonymity as the issue is a sensitive one. “He (Choi) also has been leading a lot of policy meetings to stabilise financial markets which has been visible,” the source added.

At a parliament session on December 17, Choi testified that he “strongly objected” to Yoon’s plan to declare martial law since it could wreak havoc on the economy, and said he was ready to step down as soon as the economy stabilised.

Choi has a bachelor’s degree from the Seoul National University law school, where Yoon also studied around the same time.

His career in government service has been mostly at the finance ministry, overseeing economic policy-making, financial market policies, and external business relations.

He is expected to stay acting president for months since the Constitutional Court has 180 days to make a decision on whether to remove Yoon or reinstate him.

If the court decides to remove Yoon, presidential elections must be held within 60 days.