World number one McIlroy will play with Mickelson and American Ryan Moore at 10:41am, with US Open champion Martin Kaymer in the group behind with Brandt Snedeker and Houston Open winner JB Holmes.
McIlroy and Mickelson were among the players battling for the US PGA title in near-darkness at Valhalla last year, with Mickelson and Rickie Fowler stepping aside on the 18th to allow the final group of McIlroy and Bernd Wiesberger to tee off and beat the fading light.
Tiger Woods faces a lengthy wait before he can begin his bid for a fifth Masters title.
Woods has been drawn in the penultimate group for the opening round alongside fellow American Jimmy Walker and Welshman Jamie Donaldson, teeing off at 1:48pm local time.
The 14-time major winner has started just two events in 2015, carding a career-worst 82 to miss the cut in the first and withdrawing through injury after 11 holes of the second, but said he was ready to “compete to win a golf tournament” after 11 holes of practice on Monday.
With 98 players in the field, Charley Hoffman and Brian Harman make up the first group out in the tournament proper at 7:45am, with Gary Player, Jack Nicklaus and Arnold Palmer again acting as honorary starters five minutes earlier, the legendary trio hitting tee shots on the par-four first before retiring to the clubhouse.
England’s Danny Willett will begin his Masters debut in the second group at 7:56am alongside 1987 winner Larry Mize and US amateur public links champion Byron Meth.
The final group tees off at 1:59pm and features three players ranked in the top 13 in the world, Australia’s Jason Day, Spain’s Sergio Garcia and Fowler. Fowler finished in the top five in all four majors last year.
Full tee-off times for Thursday’s opening round (all times BST):
12.45 Charley Hoffman, Brian Harman
12.56 Larry Mize, Byron Meth (Aus), Danny Willett (Eng)
13.07 Tom Watson, Camilo Villegas (Col), Gary Woodland
13.18 Mike Weir (Can), Ben Crane, Corey Conners (Can)
13.29 Vijay Singh (Fij), Darren Clarke (Nirl), Russell Henley
13.40 Jose-Maria Olazabal (Spa), Brendon Todd, Kevin Na (Kor)
13.51 Jonas Blixt (Swe), Kevin Streelman, Stephen Gallacher (Sco)
14.02 Patrick Reed, Keegan Bradley, Ian Poulter (Eng)
14.13 Miguel Angel Jimenez (Spa), Anirban Lahiri (Ind), Lee Westwood (Eng)
14.24 Bubba Watson, Justin Rose (Eng), Gunn Yang (Kor)
14.35 Adam Scott (Aus), Dustin Johnson, Antonio Murdaca (Aus)
14.57 Morgan Hoffmann, Steve Stricker, Matt Every
15.08 Ben Crenshaw, Bill Haas, Jason Dufner
15.19 Webb Simpson, Hideki Matsuyama (Jpn), Paul Casey (Eng)
15.30 Charl Schwartzel (Rsa), Joost Luiten (Ned), Sang-moon Bae (Kor)
15.41 Phil Mickelson, Rory McIlroy (Nirl), Ryan Moore
15.52 J.B. Holmes, Martin Kaymer (Ger), Brandt Snedeker
16.03 Ian Woosnam (Wal), Erik Compton, Marc Leishman (Aus)
16.14 Trevor Immelman (Rsa), Kevin Stadler, Scott Harvey
16.25 Ben Martin, Robert Streb, Cameron Tringale
16.36 Sandy Lyle (Sco), Seung-yul Noh (Kor), Bradley Neil (Sco)
16.47 Bernhard Langer (Ger), Bernd Wiesberger (Aut), Geoff Ogilvy (Aus)
17.09 Zach Johnson, Jim Furyk, Ernie Els (Rsa)
17.20 Angel Cabrera (Arg), Louis Oosthuizen (Rsa), Matias Dominguez (Chi)
17.31 Chris Kirk, Mark O’Meara, Shane Lowry (Irl)
17.42 Padraig Harrington (Irl), Ryan Palmer, Thomas Bjorn (Den)
17.53 James Hahn, Mikko Ilonen (Fin), Hunter Mahan
18.04 Matt Kuchar, Brooks Koepka, Graeme McDowell (Nirl)
18.15 Henrik Stenson (Swe), Jordan Spieth, Billy Horschel
18.26 Fred Couples, Branden Grace (Rsa), Thongchai Jaidee (Tha)
18.37 Victor Dubuisson (Fra), Luke Donald (Eng), John Senden (Aus)
18.48 Jamie Donaldson (Wal), Tiger Woods, Jimmy Walker
18.59 Jason Day (Aus), Sergio Garcia (Spa), Rickie Fowler