Last-gasp Smith stars as England shatter Ireland's Grand Slam dream
There were more than 80 minutes on the clock when replacement fly-half Smith landed the winning kick as England ended a run of four straight defeats by Ireland.
Victory was no more than England deserved given they outscored Ireland three tries to two, with this reverse just the second defeat the Irish had suffered since July 2022 following an agonising quarter-final loss to New Zealand at last year's World Cup.
Ireland, however, can still make sure of retaining their title with victory at home to Scotland next Saturday.
England were 17-8 behind early in the second half when Ireland wing James Lowe scored the first of his two tries.
But England hit back with tries from George Furbank and Ben Earl to lead 20-17 against an Ireland side reduced to 14 men after captain Peter O'Mahony was sin-binned.
Lowe's second try, however, edged Ireland two points ahead and, after England replacement Elliot Daly was just off target with a long-range penalty moments after coming on, it seemed the Irish had done enough.
But England, making good on captain Jamie George's pre-match promise to "defend our home" kept playing and were rewarded with a win that revived their title hopes following a 30-21 defeat by Scotland last time out.
England dominated territory and possession in the first half, with centre Ollie Lawrence scoring the only try of the opening 40 minutes.
Yet Ireland still led 12-8 at half-times thanks to four penalties from fly-half Jack Crowley.
Ireland kicked-off knowing a draw would be enough for them to retain their title after Scotland's 31-29 defeat by Italy earlier Saturday.
Crowley kicked them into a third-minute lead but barely 60 seconds later England hit back with a well-worked try.
Furbank ran the ball across field following a rushed clearance kick by Lowe.
England wing Tommy Freeman crashed into Ireland's Calvin Nash before Henry Slade released fellow centre Lawrence for a try in the corner.
Fly-half George Ford could not convert but England still led 5-3.
Quick passing from scrum-half Alex Mitchell, who missed England's 30-21 defeat by Scotland through injury, gave the hosts' attack a much-needed sharper edge.
An exchange of penalties between Ford and opposing stand-off Crowley left England 8-6 ahead.
Lawrence almost had a second try in the 24th minute when he appeared to regather his clever grubber-kick behind Ireland's defence. But the score was disallowed for a preceding knock-on by Furbank.
Ford missed a penalty but Crowley punished two further England infringements to leave Ireland with a slender four-point lead at the interval.
But Ireland were nine points ahead early in the second half when, after regathering a high kick in midfield, they worked an overlap out on the left as Slade was caught out of position, with a diving Lowe going in for a try at the corner.
Crowley couldn't convert, but Ireland now led 17-8.
But it took England just four minutes to respond, with good handling from lock Maro Itoje paving the way for Furbank's try out wide.
Ford was again off target from the tee and Ireland were 17-13 ahead.
But soon afterwards flanker O'Mahony was shown a yellow card for diving over the ball and Earl ensured England made their man advantage count with the team's third try.
Lowe then went in at the corner in the 73rd minute only for Crowley to make a horrible mess of the conversion in what turned out to be a significant error.