The midfielder's move to Anfield was tonight confirmed by both clubs.
Wijnaldum had been on Merseyside for a medical after agreeing terms with Liverpool
DONE DEAL: Liverpool confirm £25m signing of Gini Wijnaldum from NewcastleThe 25-year-old had made it clear that he wanted to leave St James's Park in the wake of the club's relegation to the Championship.
And United managing director Lee Charnley said: "We made it very clear at the beginning of the summer that we had no need to sell for financial reasons, despite relegation, and would only consider selling a player if it was in the best interests of the club and the team.
"After discussions with Rafa, it was felt that this particular deal was one such circumstance and would be in the best interests of both parties.
"Gini leaves with our very best wishes for his future career."