In 2009, he played primarily with the Arizona League Dodgers and in 2010 was with the Great Lakes Loons where he was 12–9 with a 2.88 ERA in 26 appearances (23 starts) and stuck out 114 batters.

On August 25, 2012, Webster was traded to the Boston Red Sox along with infielder Iván DeJesús, Jr., first baseman James Loney, and two players to be named later, in exchange for first baseman Adrián González, pitcher Josh Beckett, outfielder Carl Crawford, infielder Nick Punto, and $11 million.

Eventually, pitcher Rubby De La Rosa and OF/1B Jerry Sands were the two players to complete the trade.

On December 12, 2014, the Red Sox traded Webster, Rubby De La Rosa, and Raymel Flores to the Arizona Diamondbacks in exchange for Wade Miley.

[7] He was released by the Pirates on December 16[8] and shortly afterwards signed a one-year contract with the Samsung Lions of the KBO League.

[10] He made 12 appearances (11 starts) for the Triple–A Round Rock Express, registering a 4–4 record and 6.79 ERA with 44 strikeouts across 58+1⁄3 innings pitched.

In his first relief appearance for the Cubs on April 6, the first batter he faced, Milwaukee's Ryan Braun, hit a three-run homer.

However, the Senators' 2020 schedule was canceled, along with that of every other Minor League Baseball team because of the COVID-19 pandemic,[19] and Webster was released by the organization on May 31.