Gallagher was looking for a loan somewhere to get first team football with being so far down the pecking order at Ewood Park.
Pilgrims boss Paul Sturrock is looking forward to working with the 24 year old.
"He is a six-footer, which is important, and gives us a range of attacking options. He has the advantage that he can play in a variety of forward positions," Sturrock told the club's official website.
Gallagher is relishing the prospect of getting some regular action under his belt.
"I am looking forward to getting some games under my belt and helping Plymouth climb the table."