The 32-year-old began his career as a youth player at Southampton before he played for Swindon Town, Sheffield United, Reading, Millwall, Portsmouth, Bristol City, CSKA Sofia, Birmingham City, Oxford United and Eastleigh.
Howard made 131 appearances for Barnsley, and scored a last-minute winning goal against Liverpool in the FA Cup.
“I’ve had a really good career playing for some great clubs,” Howard told Sky Sports News HQ.
“I’ve got some great memories. Some of my favourites are scoring the winning goal at Anfield, and then captaining Barnsley in the FA Cup semi-final at Wembley in 2008.
“My favourite achievement was to be voted in the Championship Team of the Tear, and Top Midfielder at the PFA Awards. I’m retiring to pursue a career in sports management to help players with their careers with the experience I have gained. I want to thank friends, family and fans that have supported me over the years.”
Howard made more than 350 professional appearances in a sixteen-year career.