The 6-foot-2, 234-pound Mosley won the Butkus Award as the nation's top linebacker in 2013 and was the SEC defensive player of the year. He started all 13 games at weak inside linebacker and was Alabama's leading tackler for the second consecutive season.
Baltimore lost linebackers Jameel McClain and Arthur Jones during the offseason.
The Ravens were also looking for a safety, but passed on Calvin Pryor of Louisville and Alabama's Ha Ha Clinton-Dix.
Before the draft, Baltimore lost a coin flip with the Dallas Cowboys, who picked 16th. Dallas took Notre Dame offensive tackle Zack Martin, a player the Ravens coveted at a position they need to fill.