Darren O'Day is a former professional baseball player who played as a relief pitcher in Major League Baseball (MLB) for over a decade. He was born on October 22, 1982, in Jacksonville, Florida, and attended Bishop Kenny High School. O'Day then went on to play college baseball at the University of Florida, where he was a standout pitcher for the Gators.

After going undrafted in the 2005 MLB draft, O'Day signed as a free agent with the Los Angeles Angels of Anaheim. He spent the next few years bouncing around various minor league teams before finally making his MLB debut with the Angels in 2008. However, he was soon released by the team and picked up by the New York Mets, where he spent the rest of the season.

In 2009, O'Day signed with the Texas Rangers, where he would spend the next four seasons. He quickly established himself as one of the team's most reliable relief pitchers, posting a 1.94 ERA in his first season with the team. O'Day was a key member of the Rangers' bullpen during their run to the World Series in 2010 and was named an All-Star in 2012.

After the 2012 season, O'Day signed a two-year contract with the Baltimore Orioles. He continued to be a dominant force out of the bullpen, posting a 1.70 ERA in his first season with the team. O'Day was a key member of the Orioles' bullpen during their playoff runs in 2014 and 2016.

Injuries began to take a toll on O'Day in the later years of his career. He missed most of the 2018 season with a hamstring injury and was limited to just 16 appearances in 2019 due to arm issues. O'Day signed with the Atlanta Braves for the 2020 season and was a key member of their bullpen, posting a 1.10 ERA in 19 appearances.

O'Day announced his retirement from baseball on March 28, 2021, after 13 seasons in the majors. He finishes his career with a 40-19 record, 2.51 ERA, and 600 strikeouts in 576 innings pitched. O'Day was known for his deceptive delivery and ability to get batters out with his slider. He was also highly respected by his teammates and coaches for his leadership and work ethic.