Here's the entirety of Walker's message:
Officially retired, thank you to everyone that helped me in my journey to live out my childhood dream of being a Major Leaguer, I loved & cherished every day. From Pittsburgh, NY Mets & Yankees, Milwaukee, Miami, and Philly, nothing but love to those Organizations, Cities & Fans!
Walker, who will turn 36 years old in September, originally joined professional baseball after being drafted 11th overall in 2004 by the Pirates. That he spent the majority of his career with the Pittsburgh organization was fitting, as he grew up in the area and attended Pine-Richland High School, which is about a half hour's drive from PNC Park.
Walker reached the majors five years later, in 2009, and would tie for fifth in Rookie of the Year Award voting alongside Starlin Castro the following season. (Buster Posey, Jason Heyward, and Jaime Garcia finished ahead of them both.) He eventually won hardware of his own years later, in 2014, when he took home the Silver Slugger Award for National League second basemen.
For his career, Walker hit .267/.338/.426 (109 OPS+) with 149 home runs and 32 stolen bases (on 54 attempts). Walker also accumulated 19.6 Wins Above Replacement, per Baseball Reference's calculations. His 15.5 WAR with the Pirates was the sixth most for the franchise since the last round of expansion, behind Andrew McCutchen, Starling Marte, Brian Giles, Jason Kendall, and Jack Wilson.
Walker was part of three playoff teams with the Pirates, including the 2013 squad that ended the franchise's decades-long postseason drought. Prior to that season, the Pirates had last made the tournament in 1992.