He played in Major League Baseball (MLB) for the Toronto Blue Jays and St. Louis Cardinals.

In 2008, he was promoted to the Dunedin Blue Jays, and later to the Double-A New Hampshire Fisher Cats, and finally to the Triple-A Syracuse Chiefs.

As he got older, his father would drive him more than 20 miles each way to White Marsh Park in Bowie, Prince George's County where there was more competition.

[4][5] Cecil was called up to the Toronto Blue Jays on May 1, 2009, and made his major league debut on May 5 as the starting pitcher against the Cleveland Indians at home.

Continued injury problems for Blue Jays' pitchers led to Cecil being recalled to the major leagues on June 18,[7] and he started against the Washington Nationals on June 20, filling in for the injured Casey Janssen and Roy Halladay, pitching 7 innings while allowing 3 earned runs in a no-decision, in a game Toronto lost in 12 innings.

To start the 2011 season, Cecil went 1–2 with a 6.86 ERA, which led to the Blue Jays optioning him to Triple-A, in order to make room for Chris Woodward on the 25-man roster.

Cecil did not make the Blue Jays roster out of spring training, and was assigned to Triple-A Las Vegas.

On June 19, against the Colorado Rockies, Cecil broke the club record for facing the most consecutive batters without allowing a hit, set by David Cone with 36.

[12] Cecil's hitless streak ended after 43 consecutive batters on June 25, against former teammate Yunel Escobar and the Tampa Bay Rays.

He was placed on the disabled list on September 17, ending his 2013 campaign with a 5–1 record, 2.82 earned run average, and 70 strikeouts over 602⁄3 innings.

On March 24, manager John Gibbons named Cecil the Blue Jays' closer to open the 2015 season.

[19] Cecil struggled to open the 2015 season, and lost the closer role early to rookie Miguel Castro.

[20] After yielding 8 earned runs in his previous 21⁄3 innings pitched, Cecil was again removed from the closer role on June 23.

[23] On January 15, 2016, Cecil and the Blue Jays avoided salary arbitration by agreeing to a one-year, $3.8 million contract.