Dame Melinda Simmons is leaving her post as UK ambassador to Ukraine, the Foreign Office said.
The ambassador, who has helped maintain the close relationship with Volodymyr Zelensky’s administration in war-torn Kyiv, will transfer to another diplomatic post.
She will be replaced in September by Martin Harris, who has previously served as deputy head of mission in both Kyiv and Moscow during his diplomatic career.
Mr Harris said: “I am delighted to be returning to Ukraine to lead our Embassy’s vital work in supporting the Ukrainian government and people as they defend their country and our common values.
“The UK’s relationship with Ukraine has never been stronger, and we will continue to stand with Ukraine for as long as it takes.”
Dame Melinda said she would be leaving at the end of August at the conclusion of her four-year term in the “awesome and extraordinary” role.
Mr Harris was the Foreign Office’s director for eastern Europe and central Asia from 2017 to 2022 and spent a month in Lviv earlier this year to refresh his fluent Ukrainian.
Before that he spent three years in Moscow and has also served as ambassador to Romania and a deputy director in the Cabinet Office.
His previous stint in Ukraine saw him serve as deputy head of mission and consul general from 2003 to 2008.