He made the full transition to pitcher where he was voted Freshman All American for the Seminoles. He was first drafted by the San Diego Padres but did not sign in 2008.
By his Junior year he was once again All American & was drafted in the first round by the Atlanta Braves (the 28th pick overall).
He was traded to the Minnesota Twins organization in 2013 for Ryan Doumit. In December 2014 he was drafted by the New York Mets in the Rule V draft.
Through out his minor league career he was mostly used as a starter, getting to AA & AAA ball by 2012. In 2014 he struck out 133 batters in 145 innings going 9-7 between AA New Britian & AAA Rochester.
Gilmartin made the Mets bullpen out of Spring Training 2015, debuting on April 10th pitching 2/3 of an inning in Atlanta against the Braves. He is primarily used as a late inning reliever, who throws four pitches: a fastball, a curveball, a changeup and an occasional slider only to left handed hitters.
On April 14th he recorder his first hold in a win against the Philadelphia Phillies. On April 21st he finished up a 7-1 Mets win over the Braves at Citi Field. In May he finished up two Mets losses, while making ten appearances that month.
On June 14th he earned his first victory, as the Mets rallied from behind to beat the Atlanta Braves 10-8 at Citi Field & remain in first place. In that game he pitched two scoreless innings holding down Atlanta. A week later he earned his first blown save, taking a 2-1 loss to the Braves in Atlanta.
In a long 18 inning contest in St. Louis on July 19th, Gilmartin got his first major league hit. It came in the 16th inning of the 3-1 Mets win.
In August as the Mets got hot with their new acquisitions, everyone seemed to benefit. On August 21st Gilmartin pitched 2.1 innings of work earning the 14-9 victory in Colorado against the Rockies.
Three days later, in his longest relief outing of the year he earned his third win, a 16-7 Mets win against the Phillies at Citizens Bank Park in Philly. That day he got his second base hit & scored a run.
In September he would notch a hold & then make his only start on October 1st to give the starting staff a rest in preparation of the post season.
In five innings he allowed two runs on three hits taking the 3-0 loss to the Phillies. He ended the regular season 3-2 with a 2.67 ERA, striking out 54 batters & walking 18 in 57.1 innings of work.
Post Season: Gilmartin made one post season appearance, it came in Game #2 of the World Series. He faced two batters in the 8th inning of the Mets 7-1 loss.
In his first outing in Spring Training 2016 he pitched three scoreless innings, allowing four hits with two strike outs in a start against the Atlanta Braves on March 6th. The rest of his Spring wasn't bad but he lost out the final bullpen job to Jim Henderson & started out 2016 at AAA Las Vegas.