The Pro14 giant did not have it all its own way at a lively San Mames, but persistence ultimately paid off for Leo Cullen's side as Isa Nacewa's late penalty, which put it ahead for the first time, saw it level Toulouse's benchmark tally.
Racing, which made more of a contest of it than many had suggested it would and was level at the break, had to contend with the pre-match loss of Dan Carter to injury, while Pat Lambie lasted only around three minutes before succumbing to the same fate.
With Maxime Machenaud already sidelined, it was not the full-strength Racing side that boss Laurent Travers would so dearly have wanted in the showpiece as his counterpart instead became the first man to win the title as a player and a coach.
Machenaud's replacement at scrum half, Teddy Iribaren, did himself proud in a fine showing, but in a battle of kicking from the tee it was Nacewa's effort that saw Leinster add to its triumphs in 2009, 2011 and 2012 after Remi Tales missed a drop goal with the final play.
By way of further gloss to their landmark day, Leinster also became only the second team after Saracens to win all nine of their European Champions Cup games in a season, with a Pro14 semi-final against Munster up next.
Racing suffered a double early blow, indeed the first coming even before kick-off when New Zealand legend Carter, who is leaving for Kobelco Steelers at the end of the season, was forced to pull out with a hamstring injury.
Tales took his place on the bench and quickly found himself thrust into the action when Lambie hobbled off, although some small consolation came when Iribaren kicked the French side into the lead.
Leinster struggled to find its rhythm in the opening 15 minutes but, after a promising move was halted by an interception from the offside Teddy Thomas, Johnny Sexton nervelessly drew it level from the tee.
The Top 14 outfit refused to lie down and quickly restored its advantage via the boot of the cool-headed Iribaren, but Leone Nakarawa's deliberate knock-on, for which he was fortunate not to be shown the yellow card, allowed Sexton to tie the scores on the stroke of half-time.
Racing, beaten by Saracens in the 2016 final, continued to impress after the interval and retook the lead through Iribaren, with Sexton's attempted long-ranger drawing howls of derision as it came up well short and wide.
The Ireland stalwart, who has been with Leinster for all of its successes in this tournament, soon made amends as the nip-and-tuck nature of the scoring carried on.
It was Racing that nudged ahead once again heading into the final 10 minutes thanks to Iribaren, but this time it was Nacewa — retiring at the end of the season — who provided the prompt riposte before kicking the winner at the death, Tales unable to find the target with his hopeful drop-goal attempt.