South Korea’s President Yoon Suk Yeol is to meet Rishi Sunak at 10 Downing Street to sign a diplomatic accord.
Mr Yoon began his three-day state visit on Tuesday with a welcome from the King and Queen.
On Wednesday, he will hold a bilateral meeting with the Prime Minister and sign the long-term agreement covering defence and technology co-operation.
The Downing Street Accord follows similar agreements with Singapore and Japan as the UK seeks to consolidate influence in the Indo-Pacific region.
It will include a defence agreement to boost the British and Korean militaries’ co-operation on countering smuggling in the East China Sea which North Korea relies on to evade sanctions.
South Korean first lady Kim Keon Hee will be hosted by Mr Sunak’s wife Akshata Murty.
Later in the afternoon, the president will receive a call from Labour leader Sir Keir Starmer.
In the morning, Mr Yoon is to accompany the Duchess of Edinburgh for a roundtable discussion at the Royal Society on how to strengthen the role of basic science to advance humanity.
He is expected to address the discussion.
The president will be joined by notable UK and Korean scientists and will view highlights from the Royal Society’s archives alongside the duchess.
In the evening, the president and first lady, joined by the Duke and Duchess of Gloucester, are to attend a banquet at the Guildhall hosted by the Lord Mayor and City of London Corporation.
Business and Trade Secretary Kemi Badenoch will also begin negotiations with her South Korean counterpart Bang Moon Kyu at the UK-Korea Business Forum at Mansion House on Wednesday.
They will announce £21 billion of investments committed by Korean businesses in green energy and infrastructure projects across the UK.
The UK secured a free trade deal with South Korea in 2019.
In his banquet speech on Tuesday, the King said “Koreans have created a miracle” in their journey from “wartime devastation” to a thriving country where the “industrial efficiency” he witnessed during a visit in 1992 had become the “epitome” of technological innovation.
The UK visit coincides with the 140th anniversary of diplomatic relations between the UK and Korea, as well as the 70th anniversary of the armistice of the Korean War.