Ty Kelly was a career minor leaguer, having spent 8 years there, when the Mets signed him as a free agent on November 19, 2015. He started the 2016 season playing for the Las Vegas 51s, the Mets triple A affiliate. He was promoted to the Mets on May 23, 2016 to replace the injured Lucas Duda. He made his Major League debut on May 24 as the Mets starting 3rd baseman and went 0 for 4 in the Mets 7-4 loss to the Washington Nationals. Kelly recorded his first Major League hit on May 30, a 5th inning single in the Mets 1-0 victory over the Chicago White Sox. On June 8 he hit his first home run, a two-run shot that helped propel the Mets to a 6-5 win over the Pittsburgh Pirates.
Kelly returned to the minors at the end of June, at the time he was hitting just .148. He returned to the Mets at the beginning of August and finished out the season in New York helping them win the top Wild Card spot in the National League. His most productive game in his second stint came on August 18 against the San Francisco Giants. As the starting leftfielder he went 2 for 3 with a triple and 2 RBIs, but it was not enough as the Mets lost 10-7.
Kelly appeared in 39 games for the Mets in 2016 and batted .241 with a home run and 7 RBIs. The Mets included him on their postseason roster. In the Wild Card game against the San Francisco Giants, he pinch hit for pitcher Addison Reed and singled, it was one of only four hits the Mets recorded against Giants ace Madison Baumgarner who shutout the Mets 4-0 to end the Mets season.
Ty Kelly made the Mets Opening Day roster in 2017 and made his season debut in game number 2 striking out as a pinch hitter for pitcher Josh Edgin in the Mets loss to the Atlanta Braves. It was his only appearance for the season as he was designated for assignment a few days latter and was picked up off waivers by the Toronto Blue Jays. In 40 career games for the Mets Kelly batted .237.
While with the Mets Kelly wore number 55 in 2016 and 56 in 2017.
Ty Kelly also played for the Philadelphia Phillies in 2017.