[1] At East Rowan High School in Granite Quarry, North Carolina, Parnell was primarily a third baseman.

[7] Despite having a poor record since being promoted to the Triple-A New Orleans Zephyrs, Parnell was rewarded with a call-up to the New York Mets on September 1, 2008.

He earned his first major league win as a starter in his second start on August 14, pitching six innings, giving up only three hits, and striking out seven.

On August 18, 2010, in a game against the Houston Astros, Parnell hit 102.5 MPH on the radar gun, the fastest pitch in the major leagues in 2010 up to that point.

[18] Parnell was named the Mets closer for the 2013 season due to an injury to Frank Francisco.

The next day, it was reported that Parnell tore his ulnar collateral ligament and he underwent Tommy John surgery shortly thereafter, ending his season.

[23] On January 7, 2015, Parnell and the Mets agreed to a one-year deal worth $3.7 million, and avoided arbitration.

[24] Parnell made his return to the major leagues in a June 13 win against the Atlanta Braves at Citi Field.

"[25] On August 18, 2015, after pitching poorly in a weekend series against the Pittsburgh Pirates and taking two losses, (along with a 14.14 ERA in his last 10 appearances) he was placed on the 15-day disabled list with arm fatigue.

On February 19, 2016, Parnell signed a minor league contract with the Detroit Tigers, and was invited to spring training.

[33] Parnell throws primarily a hard four-seam fastball in the mid-to-high 90s with strong tailing action.

In 2010, Parnell adopted a golden retriever–yellow lab mix from North Shore Animal League which they named "Abby.