The striker told French daily L’Equipe: “I still must pass a medical on Monday but yes, I have chosen Barcelona.
“I will sign there for the next four seasons. Nothing has been signed yet but both sides reached an agreement on Friday.
“I have chosen Barcelona for the football the play, for their history and their stadium.
“I am sad to leave Arsenal. I would have stayed there for life. I didn’t want things to happen that way but I’m also ready for a new challenge.”
Henry also wrote an open letter to fans, published in British newspaper The Sun.
He said: “It’s now or never for me – sadly it has to be now.
“Arsene Wenger has said that at this moment, he will not commit to the club past the expiration of his current deal, which finishes at the end of this coming season.
“I respect his decision and honesty but I will be 31 at the end of next season and I cannot take the chance to be there without Arsene Wenger and David Dein.
“David Dein is no longer there and there is no denying the fact that has destabilised the team and the manager.
“Barcelona are a wonderful club steeped in tradition and play beautiful football. I’m sure I will be very happy there. But I will miss the Arsenal fans dearly, they have supported me through thick and thin.”