Party of National Union's National Delegates Convection on Thursday resolved to back ODM leader Raila Odinga in the August 9 presidential contest.
The party that swept retired President Mwai Kibaki to power in 2007 made the declaration on Thursday during the top organ meeting at Bomas of Kenya.
"The Party resolved that PNU joins the Azimio La Umoja Movement for the purpose of 2022 elections," read part of the resolution.
The party also resolved to enter into a working relationship with President Uhuru Kenyatta's ruling Jubilee party and other like-minded parties.
The resolution was proposed by Jackson Muriki and seconded by Philemona Wairimu.
The party's top organ met at Bomas where it was expected to declare support for Raila Odinga's presidential bid in the August 9 polls.
The delegates were also expected to make a resolution to have PNU officially join Azimio la Umoja Movement spearheaded by Raila.
The meeting comes ahead of NDCs by the Orange party and ruling Jubilee party.
Both Jubilee and ODM will hold their two-day NDCs from Friday.
