"Donald Trump is a leader. He produces results and is ready to get tough in order to protect American jobs and families," Arpaio said in a statement released by Trump's campaign Tuesday afternoon. "I have fought on the front lines to prevent illegal immigration. I know Donald Trump will stand with me and countless Americans to secure our border."
In the same statement, Trump said he had "great respect" for the controversial Maricopa County sheriff.
"We must restore law and order on the border and respect the men and women of our police forces. I thank him for his support of my policies and candidacy for president," Trump said.
Arpaio attended a campaign event with Trump in Marshalltown, Iowa, later Tuesday.
The sheriff told CNN late Tuesday night that Heidi Cruz, the wife of Texas Sen. Ted Cruz who is Trump's top rival, had called him last month in an effort to arrange a meeting to discuss Arpaio supporting the senator.
But Trump began wooing Arpaio several years ago, the sheriff said, when he questioned the legitimacy of President Barack Obama's birth certificate, sending Arpaio a note praising his efforts.
Asked about Cruz's argument last week that Trump favors "touchback amnesty"
-- a claim that Trump would deport undocumented immigrants only to allow them to come back over the border -- Arpaio dismissed the concern. He said any undocumented immigrant returning to the U.S. after being deported under a Trump administration would be entering only after having followed the legal process.
"I don't know what Cruz is talking about," Arpaio told CNN at the Sheraton Hotel in West Des Moines, Iowa. "They would have to go through the process like anyone else ... That's coming back legally."
Arpaio -- who rose to conservative fame with his aggressive roundups of undocumented immigrants and attention-grabbing tactics like clothing inmates in pink underwear -- previously signaled his support for Trump when he introduced the mogul at a Mesa, Arizona, rally late last year. Arpaio told the crowd that Trump had taken a tough stance on illegal immigration at a time when "nobody else had the guts to talk about it."
But he stopped short of endorsing Trump in his home state, saving his endorsement, perhaps, for a more pivotal time in the campaign when voters would be paying more attention.
Trump's provocative rhetoric on immigration was one of the first issues to galvanize voters around his candidacy when he launched his campaign. At first, it seemed as though he might have gone too far -- even for Arpaio's taste -- with his suggestion that immigrants coming across the border from Mexico were rapists and murderers
In an interview last September, Arpaio told Fusion's Jorge Ramos
that while there are murderers and rapists coming across the border, "I don't think the majority of people from Mexico are rapists and murderers."
In the exchange with Ramos, he also seemed to raise questions about the feasibility of Trump's plan to deport some 11 million people who are in this country illegally.
"It's not knocking doors down and dragging people out, but when you come across someone in violation of state law, then yes, you deport them. It's very simple," he said. "If the illegals don't get caught doing anything wrong, they're not going to get deported."
Former Maryland governor and Democratic presidential candidate Martin O'Malley -- who has frequently criticized Trump's immigration proposals -- blasted
Arpaio's announcement Tuesday afternoon.
".@realDonaldTrump & @RealSheriffJoe represent hate mongering at its worst. Outrageous to visit Marshalltown & promise to rip families apart," he tweeted.