[2] As his successor, the governor of Florida, Republican Charlie Crist, appointed his former chief of staff, George LeMieux.

LeMieux, who replaced Martínez in the Senate on September 10, 2009, was a placeholder and did not seek re-election, as Crist aimed at the seat himself.

However, his support of the American Recovery and Reinvestment Act of 2009 hurt his popularity among conservatives, and Tea Party candidate Marco Rubio, the former Speaker of the Florida House of Representatives, surged in the polls.

U.S. Representative Kendrick Meek was the first Democrat to declare his intention to run and he defeated billionaire businessman Jeff Greene in his party's primary.

[19] On December 1, Alex Sink declared that she would run for re-election as Chief Financial Officer rather than for the Senate.

[20] Upon Senator Martínez's not seeking re-election, early speculation surrounded former Governor Jeb Bush.

[31] In early February, speculation increased that Charlie Crist was considering running and that Martínez, who had previously pledged to serve out the rest of his term, would resign.

[32][33] The race was essentially "frozen" as potential candidates waited for Crist to declare his intentions[34][35] and almost immediately, he began to receive criticism from the right of the Republican Party.

This dissatisfaction, which had begun soon after he was elected, "snowballed" when he began considering running for the Senate, centring on his perceived moderate positions, his environmental policies, his appointment of James E. C. Perry to the Supreme Court of Florida when conservatives favoured another candidate, his willingness to give President Obama "a shot", and his support of the American Recovery and Reinvestment Act of 2009.

[39][40] However, towards the end of March, Rubio began openly criticising Crist for his support of the stimulus and expanded gambling.

[44] On April 2, Mack stated that he would not be a candidate, telling Crist: "I will be your strongest supporter and champion - regardless of whether you seek re-election or election to the Senate.

"[45] An article in The Tampa Tribune reported on the growing opposition to Crist, which quoted, among others, former state representative Dennis K. Baxley, who said that the disappointment with Crist was "the kind of disappointment that's going to have people looking in other directions for leaders... the conservative movement needs a strong leader."

Conversely, Republican consultant Adam Goodman said: "He's looked upon as such a popular and compelling figure that the sky's the limit.

Political scientist Darryl Paulson said that "Given Crist's ability to raise substantial amounts of money and his appeal to crossovers and independents, I couldn't name anybody who would have even a reasonable shot at defeating him in a primary.

[48] At the end of April, with Crist's decision nearing, he was reported to be a "near-lock" to run for the Senate[49] and, in the wake of moderate Republican senator Arlen Specter of Pennsylvania's switch to the Democrats, speculation began about whether there was "room" in the party for a moderate like Crist.

[51] After widespread speculation that he would resign before the end of his term,[52] Martínez stated that he would do so on August 7, 2009, leaving Crist in the position to appoint a replacement.

Democrat Kendrick Meek expressed disappointment, asserting that Crist should have appointed someone qualified rather than one of the top names "in his cell phone."

[55] Former New Hampshire Senator Bob Smith, who had barely featured in opinion polls, withdrew from the race on March 30, 2010, citing poor fundraising.

[59] Speculation began that Crist would drop out of the Republican primary and run as an Independent before April 30, the Florida filing deadline.

Representatives Allen Boyd, Kathy Castor, Ron Klein, Kendrick Meek, Debbie Wasserman Schultz and Robert Wexler, State Senators Dave Aronberg and Dan Gelber and Mayor of Orlando Buddy Dyer.

[28] In March, it was reported that while Gelber was "consumed" with the legislative session, Meek was raising money and collecting endorsements, including from former president Bill Clinton.

Gelber replied, "Frankly the practicality is, it's just hard to find hours in the day to make phone calls right now.

[128] Upon Chief Financial Officer Alex Sink's decision to run for governor,[129] State Senator Dan Gelber formed an exploratory committee.

[131] Term limited North Miami mayor Kevin Burns, also declared himself a candidate for the Senate seat.

[64] Organizations These candidates have gotten at least 5% in pre-election polling qualified either by paying filing fee or with the 112,446 signatures to appear on ballot.