The 27-year-old Englishman spent last season on loan from Macclesfield at Floriana of Malta after spells at Tranmere and Wrexham.
Inverness boss Terry Butcher said: "Carl has been showing his paces with us and we've liked what we've seen.
"He's very solid and an excellent tackler and I'm very pleased he's accepted a contract offer.
"He gives us another good option in defence where we have more strength in depth than at any time since I came here."
Tremarco was on the bench for Caley Thistle's 2-1 victory over Brora Rangers in midweek.