The 30-year-old will now remain at the club until the summer of 2018.
After leaving Leyton Orient, Legzdins signed a two-year contract back in June 2015 with an option of a further 12-months in the Club’s favour. That additional year has now been triggered.
The Penkridge-born stopper began his career at Blues without making a senior appearance but he has since gone on to represent nine different clubs.
Loan spells at the likes of Oldham Athletic, Macclesfield Town and three temporary stints at Halifax Town provided the six-foot stopper with first team experience early in his career.
Further moves to Crewe Alexandra, Burton Albion and Derby County saw Legzdins establish himself as a recognised Football League goalkeeper.
His playing time at Brisbane Road was limited due to injury and he rejoined Blues as a free agent two seasons ago.
With over 175 appearances to his name, including 13 during the 2016/17 campaign, Legzdins will be aiming to add to his tally when he checks in for pre-season later next month.