England finally got it right at the final hurdle, crushing previously unbeaten Ireland 42-6 at Lansdowne Road.
And it sets England up perfectly for the rest of a huge year, which will now continue with summer Tests against New Zealand in Wellington and Australia in Melbourne during mid-June.
England firmly underlined their status as world rugby's officially-ranked number one team, recording a victory that was emphatic as they ran in five tries from Will Greenwood (2), Mike Tindall, Dan Luger and Dallaglio himself.
"This game was evidence that we can produce the goods when required. I think that we've answered a few critics," Dallaglio said.
"We showed a lot of heart in what was a very tough game. Ireland put us under a lot of pressure and, in the end, it was determination that got us through.
"This is a huge year and this has given us a platform to build on.
"People have questioned our ability away from home, but to win a Grand Slam decider in Dublin 42-6 answers that."
England have now equalled their own record of 11 successive Tests unbeaten and ended an eight-year wait to be crowned Grand Slam champions.