Waddingham and Spital councillor Jeff Summers looks set to replace Coun Burt Keimach as leader of West Lindsey District Council.
Coun Keimach - who has been leader for the past three years - said he was “struggling” to find out why Conservative councillors voted for Coun Summers to be their party leader.
The Market Rasen councillor said he was “disappointed” at the decision.
He said: “It’s a shame, I’ve given them three years of success - we’ve saved hundreds of pounds for the ratepayers.”
He added: “I don’t know how they’re going to be able to cope.”
Coun Summers - who had been deputy leader - said: “I am naturally grateful to the Conservative group for electing me in to be their leader. Such a position is both an accolade and a responsibility.”
Coun Summers will be the majority group’s nominee for leader at WLDC’s annual meeting on May 20.