As Jason Day's hopes perished with a deflating front nine, and after some inevitable twists and turns, McIlroy ground out a one-shot victory over storming world No.1 Scottie Scheffler with a closing one-under par 71 on Sunday.
Despite being the first player since 1942 to go bogey-free over the weekend, Scheffler had to settle for second after a scintillating final-round 68.
Three-time runner-up Justin Rose can add a an equal-third to his CV after relinquishing a back-nine lead to finish two strokes behind McIlroy's 12-under winning total after a final-round 70.
After starting with a share of the 54-hole lead with Cameron Young, and briefly falling two shots behind sentimental favourite Rose, McIlroy steadied to become the first back-to-back champion since Nick Faldo in 1990.
Having completed the fabled career grand slam with an epic play-off victory last year over Rose, McIlroy now joins legends Jack Nicklaus (1965-66), Tiger Woods (2001-02) and Faldo as only the fourth player to go back to back.
And in capturing a sixth major championship, the 36-year-old Northern Irishman climbs above Australian Peter Thomson, Seve Ballesteros and modern-day rival Brooks Koepka among the pantheon of greats.
McIlroy joins Faldo, Phil Mickelson and Lee Trevino on the all-time list, with the seven majors secured by Bobby Jones, Gene Sarazen, Sam Snead and Arnold Palmer next in his sights.
With a disappointing, birdie-less three-over 75, Day slumped from tied fifth to joint 12th at five under - seven shots behind McIlroy.
Tellingly, though, the top-12 finish earned Day an invite back next year for what would be the one-time runner-up's 16th Masters tilt.
Adam Scott, the 2013 champion and only other Australian to make the halfway cut, tied for 24th at two under after a final-round 70.
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