The 25-year-old, who joined on a permanent basis last January following an initial loan spell from Peterborough, has made the right-back spot his own and helped the club to the League One title last season.
He has scored four goals in 30 games this term and has now played 57 times in all competitions, all of them in the starting line-up.
Manager Paul Lambert told the club's official website: "He deserves it for the way he's been playing. He's come from Posh and has done really well since he's been here. He's a top professional in terms of his training and the way he plays the game and I'm pleased for him and the club."
Martin added: "I'm delighted to have signed a new contract. I love it here and we're doing well and heading in the right direction. Playing under this manager, at this club and with the players I have around me I feel like I have improved and hopefully people can see that.
"This new contract gives me a platform to continue that and the fans have been great since I've been here and I'm hopefully here for a few more years to come."
Source: PA
Source: PA