He has a brother, Bryce (who had a successful college baseball career for the Nebraska Cornhuskers), and a sister, Kristen.

[6] When the Mets selected Nimmo with the 13th overall pick in 2011, he became the highest-drafted Wyomingite in the history of the Major League Baseball Draft.

On July 30, Nimmo posted the first four-hit game of his career, falling just a triple short of the cycle, with three runs scored and two RBIs to lead the Cyclones in a 10–5 win over the Mahoning Valley Scrappers.

Nimmo began the 2013 season with the Class-A Savannah Sand Gnats and was ranked fourth among Mets prospects.

By April 17, Nimmo was the leading hitter in the South Atlantic League with a .447 batting average,[10] earning him a SAL mid-season All-Star nod.

[11] His numbers may have been hampered by a spacious home ballpark in Savannah that's tough on lefty power hitters, as well as a wrist injury that caused him to miss some games.

[11] Nimmo started the 2014 season with Class-A Advanced St. Lucie Mets of the Florida State League.

[13] On July 28, it was announced that Nimmo was promoted to the Mets Triple-A affiliate, Las Vegas 51s as the starting center fielder.

Nimmo was promoted to the Major Leagues on June 25 to replace the slumping Michael Conforto whose batting average had fallen to .130 since May 1.

[17] On June 27, his second game, Nimmo recorded his first hit and his first run against Washington Nationals pitcher Joe Ross and went 2-4 overall.

On July 1, he hit his first home run, a three-run homer against Jason Hammel of the Chicago Cubs, making the game 7–1 in the bottom of the fourth inning.

[19] On July 29, Nimmo was once again promoted after Juan Lagares suffered a torn thumb ligament and undertook surgery to repair the injury.

[22] The injury left him unable to join the Mets Opening Day roster, and when he recovered in late April, he began his season in the minor leagues.

[28] He was later found to have a bulging disk in his neck and went through a rough rehabilitation assignment,[29] not appearing in the Mets' lineup again until September 1.

[31] He returned to the active roster in July, but suffered a hamstring strain on September 4 and missed two weeks.

[36] On June 30, 2024, during a game against the Houston Astros, Nimmo hit his 100th career home run, off of pitcher Bryan Abreu.