He played in Major League Baseball for the Washington Nationals, Cincinnati Reds, Oakland Athletics, and Toronto Blue Jays.

[3] He began his professional career with the rookie ball AZL Rangers, and also appeared with the Single-A Bakersfield Blaze.

In 2009, Roark split the year between Bakersfield and the Double-A Frisco RoughRiders, pitching to a cumulative 11-1 record and 3.02 ERA with 100 strikeouts.

Roark moved back to the rotation and had the best stretch of his career, allowing only 12 earned runs over 48+2⁄3 innings in eight starts.

[6] On August 6, 2013, Roark was called up to the MLB for the first time,[7] and on the next day pitched two innings of scoreless relief, allowing only one hit.

On September 7, Roark made his first major league start against the Miami Marlins, pitching six innings, allowing no runs and four hits, no walks, and four strikeouts, getting the win.

[8] Roark's dominance continued with a September 17 start against the rival Atlanta Braves in which he pitched seven innings and allowed no runs on just three baserunners.

[10] On April 26, 2014, Roark threw his first career complete-game shutout (with a perfect game until the 6th), allowing only 3 hits in a 4–0 win over the San Diego Padres.

[10] Roark was added back to the starting rotation in 2016, and he responded by establishing a career bests in wins (16), ERA (2.83), innings (210) and strikeouts (172).

[16] With the 2020 Toronto Blue Jays, Roark appeared in 11 games, compiling a 2–3 record with 6.80 ERA and 41 strikeouts in 47+2⁄3 innings pitched.

[21] After posting a 2.14 ERA in 24 appearances (three starts) for the Gwinnett Stripers, Roark elected free agency on September 5 when he was outrighted off of the 40-man roster.