ACADEMY product Garmston had his first professional contract extended by a further year in May 2014.
The full-back missed a significant part of the 2013/14 season through injury but was handed his Republic of Ireland Under-21s debut in a 1-1 draw with Qatar in May 2014.
He enjoyed a successful loan spell with Colchester during the second half of the 2012/13 campaign.
He made 13 appearances, including three as a substitute, for the U's to help them avoid relegation from League One by three points.
He remains a strong personality within Albion's Development squad and was part of the team that won the 2013/14 Birmingham Senior Cup.
Alan Irvine included him in his senior squad for the 2014 pre-season training camp in California.