The 24-year-old completed her move after passing her medical on Thursday morning, before signing her contract at the Camp Nou.
“This is obviously one of the best clubs in the world. The team has a great history and wonderful football mentality,” said Oshoala.
“I am excited about playing with Vicky Losada again. She’s a great midfielder, with a lot of energy and skill. I also met Fabiana in China and she helped me to make this decision”.
“My goal is to strengthen the team and help them to win and make history. This is a fantastic opportunity because I’m sure something big will happen here.”
She has been handed jersey no. 20 and is in line for her debut when Barcelona host Albacete on Sunday.