A source familiar with Sessions's plans said that the former Alabama senator "will come out forcefully in support of [President] Trump's agenda while denouncing Democrats' impeachment efforts. And steps have already begun to hire campaign staff."
Three sources familiar with the plans said the announcement would be made Thursday, with multiple sources saying it would be made during an appearance on Fox News on Thursday evening.
The deadline to file for the Senate race is Friday.
Sessions has hired OnMessage as his consulting firm for the campaign, according to two sources. OnMessage did not immediately respond to a request for comment.