The Jayhawks announced the move Monday, saying Roberts will replace Danny Manning, who is now the head coach at Tulsa.
Roberts, who joined Florida's staff in 2011, has a long-standing relationship with Jayhawks coach Bill Self. He spent nine seasons as an assistant under Self at four different schools from 1995-2004, including one season at Kansas (2003-04). Roberts' son Niko is a rising junior walk-on at Kansas.
"He's known (Self's) family for 10 years," coach Billy Donovan said. "He was up front with me throughout the whole process."
In addition to Kansas, Roberts worked with Self at Oral Roberts, Tulsa and Illinois. Roberts left Kansas following the 2003-04 season to become the head coach at St. John's. He led the Red Storm to an 81-101 record and one NIT appearance in six seasons.
Donovan said he will begin searching for a replacement immediately.
Information from The Associated Press was used in this report.