Pietro Terracciano saved from Michail Antonio in the opening minute, and West Ham took courage for a while, hurrying Fiorentina and preventing them from building from the back. Declan Rice fired just wide from the edge of the box, but the Viola pressed and passed more effectively as a stop-start first half went on.
Luka Jović had a shot blocked at source in the box, and got behind the Hammers' defence in the final seconds before the break. The No7 reacted sharply after Christian Kouamé's header looped back to him off the post, but the effort was ruled offside.
The second half sparked into life after West Ham were awarded a penalty, Cristiano Biraghi handling a long throw into the Fiorentina box. Said Benrahma struck it sweetly into the top corner, sending Terracciano the wrong way.
Their lead lasted just five minutes, though, Giacomo Bonaventura controlling Nicolás González's knock-down and then beating Areola with a low angled shot. It might have got even better for Fiorentina three minutes later, Rolando Mandragora flashing a powerful shot just wide from the edge of the box.
However, the momentum drained away, and extra time looked to be looming when Areola saved Sofyan Amrabat's hopeful effort from distance. There was a final cruel twist for the Viola, though, Jarrod Bowen chasing Lucas Paquetá's smart ball through the Fiorentina defence before angling the ball past Terracciano.
Laufenn Player of the Match: Jarrod Bowen (West Ham)
"Even when they were not on top, he was the outlet for West Ham's counterattacks and then scored the goal to win the match."
UEFA Technical Observer Panel
Paolo Menicucci, Fiorentina reporter
Football can be cruel. Fiorentina dominated possession for the whole game and were the more dangerous side with the ball and created more chances to score but a sudden counterattack is all it takes to destroy a dream. Fiorentina have reached two finals this season and lost both of them, but Vincenzo Italiano and his players should be proud of the way they have played, even though they failed to win any trophies.
Lynsey Hooper, West Ham reporter
The Hammers only held on to their initial lead for a matter of minutes. Despite a rocket of a penalty from Benrahma, the momentum shifted when Fiorentina equalised. The match was anyone's at 1-1, but Bowen was quickest to a through-ball and kept his composure to beat the goalkeeper in the final minute of normal time. The image of David Moyes running down the touchline will live long in the memory, as will this European title victory.
Jarrod Bowen, West Ham forward, speaking to BT Sport: "I dreamed of scoring but to score the winner in the last minute, I thought I was going to cry. I'm just happy, I can't put it into words. We haven't had the best season, myself included. I'm over the moon. You make that run ten times and you might get it once. I had a lot of time but I was confident and when I saw it going in, I didn't know what to do. This was the biggest game of my career."
Declan Rice, West Ham captain: "When Jarrod ran through on goal I said to myself: 'This is your time'. And then you see the ball hit the back of the net. I'm still in shock now. Honestly, it's incredible."
David Moyes, West Ham manager, speaking to BT Sport: "This year we've gone unbeaten in Europe, which is incredible. Being in the Europa League next season will be a thrill again. The moments when you win in the last minute of the game and get to celebrate with your family don't happen often. It can go against you but tonight is a brilliant feeling. This competition has been great for us; the players have been remarkable."
Vincenzo Italiano, Fiorentina coach: "We lost two finals when we played really well and it's a shame. Tonight, I honestly didn't imagine it could finish like this. We played well, had chances, equalised straight away after a penalty that could have killed us. We responded, we had a great chance through Mandragora. Then a ball came down the middle, we did not make the right movement in defence and it was all over. The lads were destroyed."
Cristiano Biraghi, Fiorentina captain: "It's so awful to lose like this. We are dead inside, above all because we are the players on the pitch but we were playing for a city, for the fans, the people who came to us after the Coppa Italia final [a 2-1 defeat against Inter] to tell us how much Fiorentina mean to them. The biggest regret is not taking anything home for them."
Joe Cole, BT Sport
"We've seen all the outpouring of emotion: I've never seen so many grown men cry. It's incredible. It's one of the most iconic scenes in this club's history."
Key stats
West Ham have won their first major continental trophy since the 1964/65 European Cup Winners’ Cup.
The Hammers made it through the whole campaign unbeaten; their final record W14 D1.
David Moyes is the first Scottish coach to win a UEFA competition since Sir Alex Ferguson claimed his second Champions League title with Man United in 2008.
Fiorentina finished as the top scorers in this season's Europa Conference League with 37 goals; West Ham were second on that list with 29.
Fiorentina's Arthur Cabral was the joint-top scorer in the Europa Conference League this season on seven goals; Kouamé and Biraghi provided the most assists with five each.
Line-ups
Fiorentina: Terracciano; Dodô, Milenković, Ranieri (Igor 84), Biraghi; Amrabat, Mandragora (Barák 90+3); González, Bonaventura, Kouamé (Saponara 61); Jović (Cabral 46)
West Ham: Areola; Coufal, Zouma (Kehrer 61), Aguerd, Emerson; Souček, Rice, Paquetá; Bowen, Antonio (Ogbonna 90+4), Benrahma (Fornals 76)
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