The band will headline the entertainment before the football match between Chelsea and Liverpool, playing their 2005 single 'Living For The Weekend'.
Hard-Fi frontman and Brentford fan Richard Archer said: "We can finally say that we've played Wembley Stadium and it will be a fact.
"The FA Cup final means it's going to be a great day although it's a shame Brentford won't be there... I think we got knocked out back in 1967."
He added: "Normally it takes you a couple of numbers to get warmed up so it's going to be funny playing a gig in exactly three minutes and 30 seconds."
Bassist and Chelsea fan Kai Stephens said: "It's the first time I've been to the new Wembley Stadium so I'm hoping Chelsea will warm to the occasion."
Drummer and Liverpool fan Steve Kemp said: "Ever since we found out we were playing at The FA Cup Final I've been willing Liverpool to get through. We've been a bit of a cup team this season so hopefully we can win another."
This year's FA Cup final kicks off on Saturday, May 5 at 3.15pm live on ITV and ESPN.
> Hard-Fi interview: "It feels like our early days again"
> Hard-Fi: 'Stick from critics got to us'
Watch the Hard Fi 'Living For The Weekend' music video below: