Joe Martinez, chairman of the Miami-Dade County Commission, made his candidacy for the county’s top job official Thursday, setting up political showdown with Mayor Carlos Gimenez.

Martinez, who had long said he would seek the mayor’s post, will challenge Gimenez in the August primary. Martinez submitted paperwork to open a campaign account Wednesday.

“I promise to listen to the needs of the residents and respond with honesty and humility,” he said in a statement Thursday.

And, setting the tone for what is likely to be a bruising battle between two County Hall veterans, Martinez indirectly attacked Gimenez for leaving his commission post to campaign for mayor in a special election last year following the historic recall of Mayor Carlos Alvarez.

“Many took advantage of this opportunity for personal ambition. I could not,” Martinez said. “However, there is and has been a void in leadership. Miami-Dade County does not need a bureaucrat running the county.”

Before becoming a county commissioner, Gimenez worked as Miami’s fire chief and, later, city manager.

“Although not a surprise to County Hall political insiders,” Gimenez said in a statement about Martinez’s announcement, “I firmly believe that this is not the time to start talking about mayoral politics, especially in light of the many challenges we face as a community. … I stand on my record.”

Martinez, who owns a private security company, worked for 17 years as an officer in the Miami-Dade Police Department, rising to the rank of lieutenant. Since 2000, he has represented County Commission District 11, which covers a wide swath of unincorporated neighborhoods in Southwest Miami-Dade, including Country Walk, the Hammocks and Kendale Lakes. He became commission chairman for the second time in November 2010.

He will run for mayor instead of seeking reelection to his commission seat. One well-known candidate has already declared his candidacy to replace Martinez: former state Rep. Juan Carlos Zapata, who has put up a smattering of yard signs in the district.

In an interview last week, Martinez told The Miami Herald he was waiting to file until after Tuesday’s high-stakes commission meeting. That’s when the board agreed by one vote to raid a fund that pays health-insurance claims and impose an additional, 4-percent healthcare contribution on county workers — bringing their total contribution to 9 percent — to balance the county budget and avoid layoffs.

Martinez voted against the plan, which will likely become a flash point in his race against Gimenez.

A portion of a memo Martinez sent the mayor last Friday sounded like campaigning already, with Martinez deriding the lead-up to Tuesday’s meeting as pitting “neighbor against neighbor, the public sector against the private sector.”

“The vitriol spewed on radio talk shows is indicative of the odium created by the inability to reach an agreement in these negotiations,” he wrote.

Gimenez responded directly to that line in a subsequent memo he sent commissioners early Monday. “Sometimes, one man’s vitriol is another man’s demand for consistent governance,” he wrote.

Still, the two men, both Republicans in nonpartisan posts, have said separately in recent weeks that they get along. They have even played a couple of rounds of golf together.

“We’re pretty much always on the same [side of issues],” Martinez has said, calling himself “a little bit more socially conservative.”

“It’s not personal,” Gimenez has agreed, noting that Martinez backed the mayor’s 2004 commission campaign.

Gimenez has raised nearly $600,000 since his June election, entirely through his political committee, Common Sense Now. Martinez has said he will also raise funds through a committee, which, unlike an individual campaign account, can accept unlimited campaign contributions.

Martinez has ties to an existing committee, Get It Done, which in the last three months of last year raised $57,750. The committee is registered to Pedro Diaz, the son of Martinez’s former district coordinator.

When The Miami Herald polled registered voters about the upcoming mayor’s race last week, more than half of the poll’s respondents said they were undecided.

Gimenez’s support stood at 27 percent, and Martinez’s at 8 percent, with a slew of lesser-known candidates coming in at lower numbers. The poll was conducted by Bendixen & Amandi International for The Miami Herald, El Nuevo Herald, WFOR-CBS 4 and Univisión 23.

In a separate poll question, about a third of respondents said they would vote today for Gimenez’s reelection. Slightly less than a third said they wouldn’t, and 38 percent were undecided.