The Eagles thought they had grabbed a 17-16 victory themselves when Jake Elliott's 48-yard strike from the field was good with just eight seconds to play at a raucous Tottenham Hotspur Stadium.
But Jacksonville's Ameer Abdullah made up 53 yards on the returning kick-off to incredibly put the Jaguars in striking range ahead of the buzzer.
Little nailed the kick and it flew between the posts as time expired, prompting the entire Jaguars sideline to burst onto the field in celebration.
It came the hard way for Jacksonville (4-1), who had been hurting themselves by racking up 100 penalty yards from 13 penalties against wounded Philadelphia (2-3).
Jacksonville's star quarterback Trevor Lawrence faced plenty of Eagles pressure, but found his groove as he threw 331 yards and recorded two touchdowns.
"One of the craziest games, maybe the craziest games I've ever been a part of, and I've been in some pretty wild ones," Lawrence said.
"Just how cool is this sport? The game's never over.
"But just the belief of our kick-off return unit, Ameer (Abdullah) being smart, breaking through, and still getting down at the second. So many things had to happen."
Wide receiver Parker Washington caught six passes for two touchdowns, including a stunning one-handed catch in the end zone from a deep Lawrence pass.
Lawrence's counterpart Jalen Hurts completed 21 of 40 passes for 220 yards and his sole passing touchdown was a 62-yard launch to Darius Cooper, which gave Philadelphia a 14-7 lead at half-time.
Philly takeover
Jacksonville have made playing in London a tradition rather than a novelty since 2013, with Philadelphia returning for the first time since 2018, when they beat the Jaguars at Wembley Stadium.
The Jaguars were the designated home team, but the stadium bowl was a sea of Philly green as the Eagles were serenaded and opponents jeered as the teams hit the field for warm-ups.
The contest started with immediate chaos from kick-off as Jacksonville's Bryan Thomas Jr and Philadelphia's Jeremiah Trotter Jr were ejected just 13 seconds in for fighting at centre field.
Meanwhile, Jacksonville's Josh Cameron thought he ran in a monster 90-yard touchdown, before that was chalked off for offsetting penalties against both teams.
Neither offence was clicking, but the Jaguars scored the game's first points at 9:34 in with Washington darting away for a 51-yard touchdown.
Washington toasted the play by bringing out Wayne Rooney's iconic knockout celebration in the end zone.
Philadelphia capitalised on an interference penalty against Travis Hunter in the second quarter to level the game via a Will Shipley touchdown, as he snuck two yards through the Jaguars scrum.
The Eagles then edged ahead for the first time on the day with Hurts floating a pass to Cooper, who sprinted 62 yards untouched to make it 14-7.
Jacksonville pressed with a 17-play possession right before half-time, but Philadelphia's defence kept thwarting them at the goal line in a horrid offensive sequence.
Jalen Carter, who was proving to be a nuisance, forced a second fumble at the one-yard line in a half where he had four tackles and two sacks.
Lawrence then almost connected with Brian Thomas Jr, before Eagles linebacker Zack Baun crushed Bhayshul Tuten to ensure his team went into the interval ahead.
Lawrence was hitting his target for the Jaguars and they reduced the gap to four points midway through the third frame after Little's 34-yard field goal following a 69-yard possession.
Philadelphia turned over the next possession on downs, but the ball came back to them when cornerback Quinyon Mitchell picked off Lawrence for his first-ever regular-season interception.
Thrilling conclusion
Jacksonville responded with Lawrence finding Brenton Strange in the red zone, but the Jaguars' offence would stall.
A false start and two delay-of-game penalties hindered them, prompting Lawrence to slam the ball down in anger and allowing the Eagles fans to ramp up the noise.
Lawrence could only find the back wall of the end zone, which handed Philadelphia the ball, but a quick three-and-out gave Jacksonville possession back in midfield.
The Jaguars took advantage and nudged 16-14 in front with 3:20 to play when Washington took down a super pass from 27 yards out, although the extra point was no good.
Hurts put Philadelphia in position for a potential game-winning field goal with a connection with Dallas Goedert and with eight seconds on the clock, Elliott drilled through the posts from 48 yards.
But Jacksonville came right back through Abdullah, who made up the yardage on the kick-off return to get the Jaguars in a game-winning spot with one second left.
DaVon Hamilton snapped the ball back to Little and he made no mistake from 57 yards as he fired in and stole a dramatic victory for the Jaguars at the death.
Jacksonville will look to maintain the momentum as they continue their London expedition against the Houston Texans at Wembley next Sunday.
For reeling Philadelphia – now on a three-game losing streak – they return stateside to host the Carolina Panthers.