Kottaras recently asked for his release, and after consideration, the club granted it on Monday.
Hours after the club announced the move on Wednesday, Kottaras was claimed by the Brewers after not clearing waivers.
The 26-year-old was out of Minor League options, so rather than try to pass him through waivers, Boston put him on unconditional release waivers, meaning he could be a free agent and negotiate with other clubs.
Kottaras hit .237 with 10 RBIs this past season. Acquired from the Padres in exchange for David Wells in 2006, Kottaras served primarily as knuckleballer Tim Wakefield's personal catcher in the first half of 2009, when Wakefield was named to the American League All-Star team.
Alden Gonzalez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.