That gives Crist a unique opportunity to replace a senator whose seat he is already seeking, The Miami Herald reported Saturday.
Martinez, the country's first Cuban-American senator, told supporters Friday in Orlando, Fla., he would cut his term in office short by 17 months.
"My priorities have always been my faith, my family and my country, and at this stage in my life, and after nearly 12 years of public service in Florida and Washington, it's time I return to Florida and my family," Martinez said.
Martinez had already indicated he would not seek re-election after his term expired in 2010, and Crist is considered the GOP front-runner for the job.
"Charlie's going to look for someone who's totally non-threatening, both a supporter and a friend, who won't embarrass him," Republican consultant Rick Wilson of Tallahassee, Fla., told the Herald.