Both Butler and Burrows have paid tribute to their outgoing leader on social media.
Butler thanked Nesbitt for his “leadership and service to modern and positive unionism and vision to make Northern Ireland work for everyone”.
“It was your brand of unionism that convinced me to pack up my career fighting fires and climbing ladders and to help build a better NI through politics.
“It’s been a pleasure and I look forward to working closely with you in the coming months and year,” the UUP deputy leader added.
Burrows wrote: “Mike Nesbitt welcomed me into the Ulster Unionist Party and will always have my admiration.
“He stepped up to party leadership again at a difficult time, while holding one of the most demanding ministries.
“Selfless, service-driven and stable leadership, for which he has my respect.”
