The Millers have decided to activate an extension option in his existing deal and the former Tranmere Rovers player will now be contracted at the club until the summer of 2020.
The deal is just reward for an upturn in fortunes for the centre-half following his return to the Millers from a loan spell at Accrington Stanley in January.
Manager Paul Warne said: “Icky has been brilliant and has displayed every quality that I require of my players here.
“We had an honest discussion at the start of the year (season), in which he told me he wanted to get out and play games. I totally respected that but also reminded him that I’d be keeping a close eye on his progress.
“I watched all of his games at Accrington and we spoke regularly. The reports that I received were always positive and we were more than happy to take him back in January.
“As I expected, he has continued to work hard and has subsequently earned his place in the side.”
The news follows the club’s decison to activate a 12-month clause in the contract of captain Will Vaulks.