The Hurricanes sent defenseman Steve Halko and a fourth-round pick in the 2002 draft to the Blues for the 31-year-old Hill, who played for Carolina from 1997-2000 before leaving via free agency.
Hill totaled one goal and 13 assists in 71 games over parts of two seasons with St. Louis. After suffering through an injury-plagued 2000-01, he was leading the Blues in hits with 69 in 23 games.
"We're real happy to get Sean back," Hurricanes general manager Jim Rutherford said. "This move gives us more depth on defense."
Carolina was relatively weak on the blue line, with offensive-minded Sandis Ozolinsh leading a group that includes veterans Glen Wesley and Aaron Ward, 21-year-old David Tanabe and the inexperienced duo of Marek Malik and Niclas Wallin.
St. Louis is strong at defense behind Chris Pronger and Al MacInnis.
Hill had his best offensive season with Carolina in 1999-2000, recording career highs of 13 goals and 13 assists in 62 games. He has 32 goals, 114 assists and 500 penalty minutes in 471 NHL contests.
Halko, 27, had played in just five games this season and was a healthy scratch in 18 straight and 26 overall. He has no goals, 15 assists and 71 penalty minutes in 149 NHL games, all with the Carolina-Hartford franchise.