Uehara, who turns 38 in April, was with the Rangers the last season and a half after two and half years in the American League East with the Orioles. Uehara has a lifetime 2.89 ERA that's tempered only by injury concerns: he had 37 appearances in 2012 and spent time on the disabled list with a right lat strain after making 65 appearances in 2011.
Uehara, who will wear No. 19, said through the team that the Red Sox "expressed the strongest desire to acquire me."
"First, I am really grateful for the Boston Red Sox expressing the strong desire to acquire me and giving this new opportunity," Uehara said. "Now it's my responsibility to meet their expectation and to give my best performance without getting injured."
Uehara went to the postseason the last two years, and had a rough time in 2011. He gave up five runs on five hits in three appearances between the first and second rounds. He struck out the side in his only inning of work during the AL Wild Card playoff game this year.
Fenway Park has been friendly to Uehara: he has a 2.08 ERA there in seven career outings, including 13 strikeouts and two walks in 13 innings.
"I know this team has a rich history and tradition," Uehara said. "I don't know much about Boston since I haven't had a chance to enjoy sightseeing yet, but I am looking forward to it."
Uehara's splitter is key to his success, and he altered his grip on the pitch to positive results at the end of last season. Briefly a closer in the Majors, Uehara figures to be a late-inning option as often as he's able to pitch.
Uehara twice won the Sawamura Award, given annually to the best starting pitcher in Japan, during his tenure with the Yomiuri Giants. He came to the U.S. prior to the 2009 season.
"I haven't been told any specific role," Uehara said. "My focus is always to give 100 percent to my pitching."