Henry, who turns 30 in August, was unveiled at the Nou Camp after passing a medical and putting pen to paper on a four-year deal with the Primera Liga side.
"Thierry Henry is a player we've been after for many years and now he's here," Barca president Joan Laporta told a news conference.
"Johan Cruyff wanted to sign Thierry Henry for Barcelona when he was a young player. When I was elected president in 2003 I wanted to sign him, we also wanted to sign him last year and today it is a great pleasure to see him here.
"He is one of the best players in the world and given his quality, experience and commitment he comes to Barcelona at the perfect time."
Barcelona were denied a third straight Primera Liga title on the final day of the season a week ago, losing out to arch-rivals Real Madrid on head-to-head
A great deal of soul-searching has gone on since then after a season with no silverware, and the club has moved quickly to strengthen the squad and appease the fans.
Henry was the focal point at Arsenal and their top scorer in four of the five Premier League seasons between 2001-06, though he spent much of the last campaign sidelined with injury.
He turned down a move to Barca and signed a four-year contract with Arsenal after they lost to Frank Rijkaard's team in the 2006 Champions League final in Paris.
At Barca, Henry faces the prospect of having to find a place in the one of the most feared forward lines in European football, which includes Cameroon striker Samuel Eto'o, Brazil playmaker Ronaldinho and Argentina winger Lionel Messi.