As Jason Day's hopes perished with a sinking 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.
"We did it again," McIlroy said to his father as he embraced his family by the 18th green.
Despite being the first player since 1942 to go bogey-free over the weekend, Scheffler had to settle for second after a final-round 68 followed his Saturday 65.
"I played what I felt was really solid on Thursday," Scheffler said.
"Then Friday, with the softer greens, that round really hurt, especially mistakes I made on the back nine.
"But overall over the weekend I put up a good fight, did a lot of good stuff in order to give myself a chance and ultimately came up a couple shots short."
Three-time runner-up Justin Rose can add 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.
McIlroy's latest green jacket success was anything but a Sunday walk in the park.
After surrendering his six-shot halfway lead with a faltering third-round 73, McIlroy found himself two behind Rose after making a nervy three-putt double bogey on the fourth hole.
His playing partner Young and fellow American Sam Burns also enjoyed the lead early in the final round.
But not even the looming shadow of a charging Scheffler could spook McIlroy as he resisted the world No.1's surge with some stellar golf of his own down the stretch.
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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