Young is in the lineup Monday night, hitting ninth.
With Young ninth and pitcher Jacob deGrom hitting eighth, it marks the first time in Mets history the pitcher has ever started a game in the eighth spot in the lineup.
To make room for Young on the roster, the Mets optioned OF Andrew Brown to Triple-A Las Vegas.
In 44 at-bats during two separate stints with the Mets this season, Brown was hitting .182 with a .245 OBP, two home runs and seven RBI.
Young was placed on the disabled list on May 25 with a strained right hamstring, and had recently completed a minor league rehab assignment that was split between High-A St. Lucie and Double-A Binghamton.
In four rehab games, Young went 1-for-10 with three walks and four runs scored.