Three state department officials will testify first. So far lawmakers from three key House committees have heard from witnesses behind closed doors.
Mr Trump denies any abuse of power.
The first public witness will be Bill Taylor, acting US ambassador to Ukraine, who delivered some of the most explosive private testimony last month.
It shows Mr Taylor told lawmakers it was his “clear understanding” that the president had withheld nearly $400m (£310m) in US military aid because he wanted Ukraine to investigate the Bidens.
Joe Biden is a Democratic front-runner for the presidential election a year from now.