The veteran ITV gameshow attracted 3.92m (17%) in the 9pm hour, adding 164k (0.9%) on ITV1 +1.
Host Chris Tarrant previously called for the return of the Who Wants to be a Millionaire? general public edition, which ITV originally axed due to poor ratings.
Millionaire managed to trump the second part of BBC One drama Blackout, which lost a hefty 1.5m on its debut last week.
BBC Two's 9pm documentary, meanwhile, performed impressively as Double Cross: The True Story of D-Day Spies interested 2.3m (10%), beating Undercover Boss's 1.72m (7.5%) for Channel 4 (+1: 293k/1.7%), and Big Brother's 1.38m (6%) for Channel 5 (+1: 133k/0.7%).
Back in the 8pm slot, Volcano Live enthralled 2.49m (10.8%) on BBC Two, while ITV1's Countryfile mustered 3.19m (14%) as well as 123k (0.5%) on +1, and Channel 5's Police Interceptors fetched 1.13m (4.9%).
For BBC One, Panorama slipped back to 2.55m (10.8%) at 8.30pm, while the continuation of the channel's elderly season saw 2.16m (14.7%) tune in for How To Live Beyond 100 at 10.35pm.
Channel 4's 8pm pairing of Dispatches (780k/3.4%) and Jamie's Summer Food (872k/3.7%) struggled to make an impact, while The Walking Dead slumped to 713k (3.9%) on Channel 5 at 10pm (+1: 103k/1%).
Overall, ITV1 comfortably led primetime with 22.5% (+1: 0.6%) against BBC One's 17.4%. BBC Two earned third place with 8.1%, ahead of Channel 4's 4.9% (+1: 0.7%), and Channel 5's 4.2% (+1: 0.3%).
BARB ratings data supplied by Attentional