Andros Townsend has completed his move to Newcastle from Tottenham after signing and five-and-a-half-year deal, the club has confirmed.
The 24-year-old England international has joined the Magpies for an undisclosed fee, understood to be £12m.
His arrival at St James' Park was confirmed in a club statement which said: "Newcastle United have completed the signing of England international winger Andros Townsend from Tottenham Hotspur.
"The 24-year-old arrives at St James' Park for an undisclosed fee and has signed a five-and-a-half-year deal with the Magpies. He will wear the number 25 shirt."
Townsend put pen to paper after passing a medical and agreeing personal terms, ending a 16-year stay at Spurs which had soured in recent months.
His first opportunity to play for his new club will come at Everton next Wednesday night, and he could make his home debut in what will be a crucial clash with West Brom three days later.
Townsend said: "I'm delighted to be here. Newcastle United is a fantastic club with great fans, a great stadium and great tradition.
"As soon as I heard Newcastle were interested in me, there was only one place I wanted to go so I can't wait to get started."
Townsend's arrival represents another boost for under-pressure McClaren, who has been desperate to add proven Premier League quality to his squad to assist in the fight for top-flight survival.
Meanwhile, a Newcastle XI is understood to have been beaten 6-0 by a Sunderland XI yesterday in a behind-closed-doors friendly organised to give fringe players, and those returning from injury at both clubs, a chance to get some game-time.