The 22-year-old Marseille winger has signed for the club.
Thauvin was identified as a potential signing by chief scout Graham Carr more than two years ago and the club has been monitoring his situation since.
However, managing director Lee Charnley has now signed the player.
McClaren was assured of significant investment in the squad when he accepted the job in June with owner Mike Ashley having signalled his intention to commit funds to the task of ensuring there is no repeat of last season's desperate fight for top-flight survival.
The arrivals of Georginio Wijnaldum, Aleksandar Mitrovic and Chancel Mbemba have gone some of the way to fulfilling that mission, but McClaren indicated last week that he was hopeful of further additions, and Saturday's 2-0 defeat at Swansea illustrated the club's enduring need for reinforcements.
Newcastle have turned to left winger Thauvin in a bid to to inject pace and invention into the team and create a fresh supply line for strikers Papiss Cisse and Mitrovic, as well as attacking midfielders Wijnaldum, Moussa Sissoko and, when he is fit, Siem de Jong.
Compatriot Remy Cabella, who has struggled to adapt to the physicality of English football, has gone in the opposite direction with reports in France suggesting Marseille want to take him on an initial loan with a view to a permanent switch as part of the deal.
The Magpies look set to go to the wire once again as they attempt to complete their business before the transfer deadline with a striker - they have spent much of the summer trailing QPR striker Charlie Austin - and defenders still on McClaren's wish-list.
They have taken just a single point from the opening two league fixtures - they drew 2-2 with Southampton at St James' Park during the opening weekend of the campaign - and travel to Manchester United on Saturday before welcoming Arsenal to Tyneside.