The Blaugrana have agreed to lock horns with their Catalan rivals at a later date than originally planned, vowing to field their "best possible team"
The two Catalan sides were due to contest the trophy on July 31, but the Blaugrana decided against fielding their first team due to a congested fixture list and risk of injury.
Their decision led to the cancellation of the match, with Espanyol CEO Joan Collet accusing Barca of showing a "lack of respect" towards his team.
The Copa del Rey winners have now confirmed that they have accepted the proposal from the Catalan Football Federation (FCF) to play the match at a later date.
"The club have always supported the Catalan Football Federation, Catalan football and ultimately Catalan sports," a Barca statement read.
"In the same way the club have supported the country in the past, like in the Marathon against Poverty or, more recently, agreeing to donate all proceeds from the upcoming match between USAP and Stade Toulousian to the victims of the Alt Emporda fires, we are committed to continuing that support in the future.
"The club accept the FCF’s proposal to play the Supercopa Catalunya on September 26. The Barcelona coaches will present the best possible team for the match.
"The club urges organisations and institutions to acknowlege that the large amount of official matches make it difficult for the team and players to take on additional commitments."
The Supercopa Catalunya against Espanyol will come three days before Barcelona's Liga contest at Sevilla, their fourth league match of the season.