The announcement of Tandy and Makowiecki brings the LMDh roster at the Porsche Penske Motorsport squad to 10 drivers, which encompasses six full-timers for the WEC and four for IMSA.
Porsche has yet to reveal how the 10 will be split across the two championships and it is understood that the final decision has yet to be make.
Tandy, who won the Le Mans 24 outright with the Porsche 919 Hybrid LMP1 prototype in 2015, is returning to the German manufacturer after a two-year absence.
The 38-year-old Briton was on the books of the marque from 2013 until 2020 before signing for Chevrolet’s Corvette Racing team after Porsche axed its factory IMSA GT Le Mans class assault with the CORE Autosport squad.
His successes during his initial eight-season stint with Porsche also included overall wins at the Petit Le Mans IMSA round in 2015 and the Spa and Nurburgring 24-hour classics in 2018 and '20 respectively.
The confirmation of the long-rumoured Porsche return by Tandy on Monday came the day after his final commitment with Corvette Racing in the official WEC rookie test in Bahrain, which followed the 2022 WEC curtain-closer.
Makowiecki has joined the LMDh squad after a season in which he has been an integral part of the test programme with the car developed in conjunction with Multimatic Motorsport.
He was the first driver to sample the 963 on both the simulator and the race track and received a name check for his contribution when Porsche announced its second tranche of LMDh drivers in June.
The Frenchman, 41, joined Porsche from Aston Martin in 2014 and claimed GTE Pro victory at Le Mans this year.
He also has a hat-trick of Sebring wins and a Nurburgring 24 Hours, all claimed together with Tandy, among his successes at Porsche.
Tandy, who is due to get his first taste of the 963 in December, said: “I couldn’t be happier or more excited to join Porsche Penske Motorsport for 2023 and feel honoured to race the 963 and be back in the top-classes once again.
“When I heard the names Porsche Motorsport and Team Penske together, it didn’t take long once the discussion started to make a decision.
“Porsche Motorsport gave me the big break in my career and my life.
“We went on to achieve some unbelievable successes together, but that is hopefully just the beginning.”
Makowiecki said: “I was involved in the development of the Porsche 963 from day one, so I’ve experienced first-hand the huge advances that we’ve made over the past few months.
“We’ve made great progress; that’s why I’m looking forward to the first races of the 2023 season.”
Porsche Motorsport boss Thomas Laudenbach described the now-completed PPM driver roster as “a force to be reckoned with”.
“With Nick and Fred, we know exactly what we’re getting: total commitment, a wealth of experience and incredible talent,” he said.
Porsche named Felipe Nasr and Dane Cameron as the first drivers for the LMDh, which will race in the Hypercar class in WEC and GTP in IMSA, last December.
They were followed by the announcement of Andre Lotterer, Kevin Estre, Michael Christensen, Laurens Vanthoor, Mathieu Jaminet and Matt Campbell on the launch of the car at the Goodwood Festival of Speed in the summer.
