The 34-year-old forward from Barcelona said Saturday on Twitter he is exercising his right as a free agent and heading east to join the playoff-contending Bulls.
"It hasn't been easy," he wrote. "After meditating it a lot, I have chosen to play with the Chicago Bulls. Looking forward to this new chapter of my career."
With Bryant out most of the season, Gasol averaged 17.4 points, 9.7 rebounds and 3.4 assists in 60 games in 2013-14. He also missed some games with a groin strain and vertigo.
He has averaged 18.3 points, 9.2 rebounds and 3.3 assists in 13 NBA seasons with Memphis and the Lakers.