Terms were not disclosed. Rams spokesman Rick Smith said the deal was reached early Friday, before the first workout of training camp.
Also expected at practice was quarterback Marc Bulger, who was a no-show for a mandatory team meeting Thursday, when players were to report. Bulger is signed through next season but is seeking a new contract and had threatened to hold out.
Carriker played defensive end at Nebraska, where he was the Big 12 defensive lineman of the year as a senior, leading the Cornhuskers with seven sacks. He is expected to move to defensive tackle for the Rams, who have struggled in recent years at that position.
Prior to selecting Carriker with the 13th overall pick in April, St. Louis also chose defensive tackles Ryan Pickett and Damione Lewis with first-round picks in 2001 and Jimmy Kennedy with a first-round pick in 2003. Only Kennedy remains on the roster.
Bulger is in the final year of a four-year, $19.1 million contract, putting him somewhere in the middle of the NFL salary for his position. The team said signing him to a new deal is a priority and has been formulating an offer that could make him the highest-paid player in franchise history.
Last year he threw for 4,301 yards with 24 touchdowns and eight interceptions, a 62.9 percent completion rate and ranked fourth in the NFL in passer rating.