The 39-year-old closer recorded 26 saves and posted a 6-5 record with a 2.52 ERA in 64.1 innings during his second season in Boston. In early September, Uehara lost his closer spot after three blown saves in six games.
He had a career best 1.09 ERA in 2013, with a 4-1 record and 21 saves in 74.1 innings. He added seven saves and one earned run in 13 and two-thirds innings in the postseason to help the Red Sox with the World Series that year.
Uehara entered free agency on Thursday but was restricted from signing with any other team until next week. The terms of his deal with Boston were not disclosed, but according to Alex Speier of WEEI.com, the new contract will pay him $18 million.
In seven seasons in the major leagues, including stints with the Baltimore Orioles, Texas Rangers, and Boston, Uehara has gone 15-15 with a 2.44 ERA, 412 strikeouts and 61 saves in 350.1 innings pitched.
Boston finished 2014 with a 71-91 record, placing fifth in the AL East.