In the impoverished area of North Dublin, local band And And And are performing crooning hits at another wedding party gig. They dream of something more. After the show, guitarist Outspan Foster, pianist Steven Clifford and bassist Derek Scully pin down wheeler-dealer and local music afficionado Jimmy Rabbitte and ask him to help them make it big. Jimmy tells them to get rid of their singer, Ray, and inject some soul into their sound.
Jimmy places an advert in the local paper and is soon deluged by scores of disastrous wannabes, from punk kids to Elvis impersonators. Everyone, it seems, is looking for a way out of their working-class rut.
Jimmy decides to put together the band from people he knows - female backing singers Bernie, Natalie and local beauty Imelda; his friend Billy on drums and Dean on Sax. Now there's just the problem of a singer. While the band were on a break at the wedding, drunken sixteen-year-old lout Deco Cuffe commandeered the microphone and let loose his amazingly powerful voice. Jimmy confronts him about it. Deco is initially resistant, but his ego gets the better of him and he agrees to join.
Just when it seems the band might be complete, Joey 'the Lips' pulls his moped up to Jimmy's door and offers his services. Joey is a veteran trumpeter, who claims to have played with Otis Redding and other soul greats. Jimmy snaps him up and The Commitments are born.
Buying musical equipment on the black market, they embark on their first rehearsal - above a pool hall whose owner is in prison. It could go better: the girls sing as if in a choir, the timing is off and Deco upsets everyone with his uncouth cockiness.
After much practice, they eventually convince the local church community centre to give them a gig, under the pretence of it being part of an anti-heroin campaign. Charging £2 to enter and with thug Mickah Wallace policing the crowd, they are all set. They draw a good crowd, who seem to enjoy the performance. Suddenly the power shorts out and the amps explode, electrocuting the bassist, Steven.
Steven is OK, but now the band have another problem - drummer Billy hates Deco so much he wants to quit the band before he ends up hitting him and thereby violating his probation. Believing anyone can play the drums, they enlist the help of livewire Mickah Wallace, who turns out to be not bad.
Time for their first proper gig outside of the local community, and the band are excited. Not only do they get to play to a larger audience, but Joey has promised that his 'old friend' - soul legend Wilson Pickett - will be along later to jam with them. On this promise, Jimmy has convinced the local press and Music Week to attend.
The gig is going excellently, the crowd are loving it and the problems seem to have been overcome. However, the band are arguing - they've refused to don their trademark black and white suits, saxophonist Dean is on a jazz kick and Deco is getting too big for his boots, claiming to have offers from other bands.
By the interval, The Commitments are getting worried about Wilson Pickett's no-show and further arguments ensue. They go back on stage and denounce their manager for misleading the audience about Wilson Pickett, but a sterling performance of one of his songs silences the crowd's protests.
However, after the gig, the fighting continues - Mickah beats up Deco outside the club, and Jimmy storms off in frustration, claiming the band is finished. Joey follows him, but is berated by Jimmy for misleading them about Wilson Pickett. Just as Joey rides off, a limousine pulls up next to Jimmy - it's Wilson Pickett asking for directions to the club. It's too late.
Later, Jimmy explains that the band's members have since gone their separate ways, their brief dream of fame ended.
