US Ambassador to the United Nations Nikki Haley announced her resignation on Tuesday.
Ms Haley, who is an outspoken supporter of the president in the diplomatic community, and a frequent critic of the UN's stance towards Israel, first discussed her resignation with the president last week.
She will be leaving the administration by the end of 2018, according to Mr Trump, who made the announcement with the ambassador in the Oval Office.
Trump said she is a "very special" person "who gets it," adding that she told him six months ago that she might want to take some time off to spend with her family. Mr Trump said that together they "solved a lot of problems" at the UN, according to the Independent report.
"She's done a fantastic job," the president said, adding the pair will be "in constant touch". Mr Trump was a frequent critic of the UN, calling it a "good time club" but today he noted Ms Haley made the ambassadorship "a more glamorous position, she's made it a more important position".