The Indiana governor is to back Republican presidential candidate Ted Cruz, four days before a crucial primary contest there, US media report.
Campaigning on Friday, Mr Cruz praised Governor Mike Pence, saying he would enthusiastically welcome his support.
Indiana’s primary on Tuesday is the Texas senator’s best chance to stem the momentum of Republican front-runner Donald Trump.
Mr Trump has won a string of states, taking him closer to being the nominee.
But if he does not win 1,237 delegates, there will be a contested Republican convention in July.
This would mean the delegates – local party activists and senior Republican officials – being free to pick an alternative candidate like Mr Cruz.
It has been an eventful week for the Texas senator, taking a beating in five state primaries, picking Carly Fiorina as his running mate and then being called “Lucifer” by ex-House Speaker John Boehner.
Mr Pence is expected to make his endorsement public later on Friday.