Ilgauskas ended his 12-year career with the Cavs and followed teammate LeBron James to Miami where, Ilgauskas said, he had his best opportunity to win an NBA championship.
Ilgauskas, whose playing time was reduced when Shaquille O'Neal arrived in Cleveland, joins Joel Anthony, Jamaal Magloire and rookie Dexter Pittman as candidates for the center job.
The 35-year-old Lithuanian averaged 7.4 points and 5.4 rebounds per game last season and is considered a solid offensive rebounder.
James sent up a welcome message via Twitter, saying he was glad "Big Z" was joining him in South Beach, The Miami Herald reported.
Ilgauskas, who played briefly with Washington last season before rejoining the Cavs, will sign for a two-year veteran's minimum of about $2.8 million, the Herald said.