2001–04 seasons Rowland-Smith began his pro career in 2001 with the
Rookie level Arizona League Mariners. In 17
relief appearances, he allowed just one
home run in
innings pitched. He appeared in 18 games (six starts) with Everett, posting a 4–1
record, a 2.77 ERA, 58
strikeouts, and 58
hits allowed in innings pitched. On 4 March, the Twins signed him to a one-year contract. He spent most of 2005
spring training with the Twins. In 23 games (one start) for the Missions, he had a 1–3 record, a 2.83 ERA, 48 strikeouts, and 38 hits allowed in innings. Griffey was the first batter Rowland-Smith faced; Rowland-Smith struck the future Hall of Famer out, proceeding to pitch 1 scoreless innings in a blowout 16–1 Mariners loss. In the first game of that stretch, he struck out six batters in four scoreless innings of relief in an 8–4 loss to the Twins. He earned his first career win 13 September against the
Tampa Bay Devil Rays, pitching scoreless innings in a game the Mariners trailed 7–1 but rallied to win 8–7. In his first year with Seattle, he struck out 42 batters in 38 innings, posting a 1–0 record and limiting opposing batters to 39 hits. He collected his first
save on 8 April against the
Tampa Bay Rays in Seattle's 6–5 win, tossing innings and retiring all five batters he faced while protecting one-run lead. His first major league start came 1 July against the
Toronto Blue Jays; Rowland-Smith threw three scoreless innings before getting replaced by
Roy Corcoran with two outs in the fourth inning after allowing three runs that inning. The Mariners rallied to win 7–6. He made three more relief appearances before being optioned to Tacoma on 20 July to be converted to a starting pitcher. He went 2–0 with a 2.89 ERA in three starts for the Rainiers, holding opponents to a .185 batting average before joining Seattle's rotation on 9 August. He faced Oakland again in his final start of the year on 27 September, allowing three runs in innings this time but picking up the win in a 7–3 victory. In 47 games (12 starts) with the Mariners in 2008, he had a 5–3 record, a 3.42 ERA, 77 strikeouts, and 114 hits allowed in innings. At the beginning of the season, Rowland-Smith started one game before being placed on the disabled list with
triceps tendinitis. He was sent to Tacoma for rehab starts, but a dismal outing on 5 June in which he allowed 12 runs in innings prompted the Mariners to option him to Tacoma. In July, he was promoted and added to the starting rotation after going 5–3 with a 4.31 ERA in 10 starts for Tacoma. He pitched seven innings in his first start back on 24 July, allowing four runs and taking the loss in a 9–0 defeat to the
Cleveland Indians. Five days later, he limited the
Toronto Blue Jays to two runs over seven innings and picked up his first win of the year in the Mariners' 3–2 victory. Three times in 2009, he threw a season-high eight innings, including a game on 16 September, when he limited the
Chicago White Sox to one run in a 4–1 victory. Rowland-Smith made his last start of the year for the Mariners on 3 October, holding the
Texas Rangers to one run over innings in a 2–1 victory. Rowland-Smith finished the season with a 5–4 record, a 3.74 ERA, 52 strikeouts, and 87 hits allowed in innings over 15 games (all starts). He struggled to begin the season, posting a 7.62 ERA in his first eight starts while losing all four of his decisions. After the shortest start of his career on 18 May, in which he gave up seven runs in innings, the Mariners moved him to the bullpen. Rowland-Smith returned to the rotation on 5 June, when
Doug Fister had to miss a start because of shoulder fatigue. The Mariners lost to the Angels 11–2, but Rowland-Smith limited the
Los Angeles Angels of Anaheim to one run in five innings. After that, he continued to be used as a starter. The win, however, would be his only victory of the year. On 27 July, he gave up 11 runs over five innings in an 11–0 loss to the White Sox. The Mariners left him in the game that long because they wanted to preserve their bullpen. After the game, he was placed on the disabled list with a lower back strain, which
Rob Neyer of
ESPN speculated was a "phantom injury" designed to get him off the roster, since the Mariners could not send him to the minor leagues without exposing him to
waivers. After a rehab stint in Tacoma, he rejoined the team in September when rosters expanded. Upon his activation from the disabled list, Rowland-Smith was mainly used out of the bullpen, except for the last game of the season, 3 October, in which he gave up two runs in five innings and had a no-decision in a 4–3 loss to the Athletics. 20 of Rowland-Smith's 27 appearances in 2010 were starts (a career-high), but only one of those was a win, as opposed to ten losses. He had a 6.75 ERA and gave up 141 hits in innings. Seattle made him their candidate because of his work in hosting the Mariners Care
Cystic Fibrosis Foundation golf tournament. On 2 December 2010, the Mariners
non-tendered Rowland-Smith, making him a
free agent.
2011–2013 seasons On 9 December 2010, the
Houston Astros signed Rowland-Smith to a one-year, $725,000 contract. He spent most of the season with the PCL's
Oklahoma City RedHawks. In 22 games (19 starts), he had a 2–10 record, a 6.19 ERA, 87 strikeouts, and 131 hits allowed in innings. He spent the whole season with the
Iowa Cubs of the PCL, where he was used more as a reliever (22 games) than a starter (eight games). He had a 3–6 record, a 3.94 ERA, 62 strikeouts, and 75 hits allowed in innings pitched. In 37 games in relief for the Triple-A
Pawtucket Red Sox, he had a 7–0 record and a 1.55 ERA.
2014 season Rowland-Smith signed a minor league contract with the
Arizona Diamondbacks prior to the 2014 season. He was excited about joining Arizona because they were opening their season with two regular-season games in March against the
Los Angeles Dodgers at the
Sydney Cricket Ground in Australia. While he did not pitch in the Australian series, Rowland-Smith was on the Diamondbacks roster at the beginning of the 2014 season, his first time on a major league roster since 2010 with the Mariners. He made his last appearance in the major leagues on 14 April, giving up two runs (one earned) in the final two innings of a 7–3 loss to the
New York Mets.
Designated for assignment on 18 April, he cleared waivers and elected to become a free agent on 21 April. In six games with the Diamondbacks, he posted a 4.91 ERA, allowing five runs (four earned) in innings of work. He pitched for the Triple-A
Buffalo Bisons of the International League, allowing 8 runs in just 14 innings before drawing his release on 11 June. On 28 June, he signed a minor league deal with the
Cincinnati Reds. He made one start for the Triple-A
Louisville Bats but was mostly used out of the bullpen, posting a 4.20 ERA in 12 games with no wins or losses. He appeared in nine games with the team, posting a 1–4 record and a 4.70 ERA in 46 innings. For winter 2015–16, Rowland-Smith pitched in one game for
Gigantes del Cibao of the
Dominican Winter League. ==International play==