Yorke, for whom United paid over £12million, said: "It can’t wait to get going. This is a new start for me and I am determined to grasp the opportunity.
"It has been a little frustrating over the past year or so, but all that is history. My aim is to get back among the goals and help Rovers move forward," he continued...
"There’s a passion deep inside me that wants to do well and I’m desperate to re-establish myself in the Premiership."
Souness is said to be "relieved" to finally have Yorke’s signature after weeks of negotiations with United.
He said: "Dwight is a player I have targeted for some time and it is tremendous news he has signed for us today.
"I am delighted. He is a top quality player with a proven track record who can only be an asset as we look to go forward."