A season that began with pleas to play in a higher competition ended with Palace's first-ever European trophy as Mateta's goal lifted his team to a 1-0 win over Rayo Vallecano in the final in Leipzig, Germany, on Wednesday (Thursay AEST).
The French forward, who was close to leaving in January before a transfer collapsed, scored on a rebound in the 51st minute after Rayo goalkeeper Augusto Batalla parried Adam Wharton's long-range shot.
Palace's win keeps English teams on track for a sweep of the three main European men's club competitions.
Aston Villa won the Europa League last week and Arsenal face Paris Saint-Germain in the Champions League final on Saturday.
It was a triumphant end to a season that began with Palace in court appealing in vain against being demoted from the second-tier Europa League, the competition it had originally qualified for by winning the FA Cup, in a dispute over ownership rules.
Palace's win lands them a Europa League spot for next season, much to the delight of departing coach Oliver Glasner, who said on Wednesday he wanted to watch the team's progress on TV next season.
Glasner announced in January he would leave at the end of the season when his contract expires. The Austrian has been in charge since February 2024 and led Palace to their first major trophy last season in the FA Cup. It's not clear yet where he'll go next.
It was the third time in the Conference League's five-season history that an English team has lifted the trophy after West Ham in 2023 and Chelsea a year ago.
Mateta's goal lit up the final after a cagey first half with no shots on target from either team.
He showed lightning-quick reactions to knock in the rebound after an initial long-range shot from Wharton, who returned to Palace's line-up after an ankle knock against Arsenal last week and was a commanding presence in midfield.
"I feel fantastic! I feel fantastic! We did it,'' Mateta told TNT Sports.
"First time in Europe, we did it! Now I just want to celebrate, I just want to party.''
Yeremy Pino came within a whisker of making it 2-0 soon after when he hit a free kick that bounced off one goal post, along the goal line and away off the second post.
Rayo's best chance came early on when Alemao skewed a volley wide of the post off a cross from Pep Chavarria.
Palace chairman Steve Parish wants the club to keep on winning silverware after lifting three trophies in a year.
"Just surviving in the Premier League is difficult, but to win an FA Cup, a Community Shield and a European title at the first time of asking is an incredible achievement from everybody. It means everything,'' he said.
- with PA
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