The Cameroon international passed a medical with Tito Vilanova’s men on Monday morning, with the news unveiled in the afternoon of a £15 million switch.
Song has expressed his delight at moving to the Camp Nou and is looking forward to getting started with his new club.
“Today is a very good day for me and my family. Very happy to be here, this is the best team in the world, playing at a club like Barca is something I wanted when I was young,” he told Barca TV, translated to English by Sky Sports.
“I hope the team will continue to win, this is a winning team. They win everything. I will give my best in training and when I get the chance to play I will do it.”
The news leaves Arsenal slightly short of central midfield options, as Song follows in the footsteps of Robin van Persie in leaving north London this summer.
By Gareth McKnight