He added: “I would not be comfortably seeking a vote knowing that privately I was intending to retire during the mandate.”
He also said: “I retook the leadership to do a short-term job of getting the party match fit for the forthcoming election campaign.
“That job is now done so the time is right to select the politician who will lead us into the May 2027 polls promoting our brand of confident, responsible unionism.”
Nesbitt has been UUP leader since August 2024 and it was his second stint in the role.
He won the contest in 2012, but quit in 2017 after disappointing assembly election results.
Since then, Robin Swann, Steve Aiken, Doug Beattie and Nesbitt again have been handed the leadership unopposed with no noticeable upturn in the once-mighty party’s fortunes.
A party spokesperson described Nesbitt’s decision to step down as a “pivotal moment”.
“Party officers will shortly outline the leadership selection process, ensuring an inclusive, engaging and seamless transition.”