The controversial sheriff who Donald Trump pardoned has announced he is running for the US Senate to help "Make America Great Again".

Former Maricopa County Sheriff Joe Arpaio – who the Justice Department claims oversaw the worst pattern of racial profiling by a law enforcement agency in US history – said he will run for the Senate in Arizona next year.

"I am running for the U.S. Senate from the Great State of Arizona, for one unwavering reason: to support the agenda and policies of President Donald Trump in his mission to Make America Great Again," Mr Arpaio tweeted on Tuesday.

The announcement puts him in the middle of a crowded Republican primary race to replace current Arizona Senator Jeff Flake – a frequent critic of Mr Trump. US Representative Martha McSally and former state Senator Kelli Ward are both vying for the seat.

Mr Arpaio told the Washington Examiner that he planned to "work hard" and not "take anything for granted" in the race.

"But I would not being doing this if I thought that I could not win," he added. "I’m not here to get my name in the paper, I get that everyday, anyway.”

Democratic National Committee Chairman Tom Perez called the announcement "sad and disturbing," and said his party would fight "tooth and nail" to prevent Mr Arpaio from holding office.

Trump defends Arpaio pardon

Mr Arpaio was Mr Trump's first pardon, and one of his first supporters. He was convicted of criminal contempt of court last year for defying an order to stop officers from detaining people based solely on suspicion of their immigration status.

The former sheriff's strict stance on immigration helped catapult him to national fame, and into the President's good graces. During his six terms in office, Mr Arpaio led a department with “a pervasive culture of discriminatory bias against Latinos,” according to the Justice Department.

Under Mr Arpaio's tenure, Latino drivers were unfairly targeted for traffic stops, and Spanish-speaking prisoners were punished for failing to understand officer's orders in English. Inmates were occasionally forced to wear pink underwear and sleep in sweltering "tent cities" as punishment.

'I can get my family back': immigrants driven out of Arizona return home Show all 3 1 /3 'I can get my family back': immigrants driven out of Arizona return home 'I can get my family back': immigrants driven out of Arizona return home Protesters outside Arizona's State Capitol in Phoenix celebrate their legal victory against the crackdown on illegal immigration Joshua Lott/Reuters 'I can get my family back': immigrants driven out of Arizona return home Campaigners with Patricia Rosas, right, who now says she can look forward to being reunited with her daughter, son-in-law and grandchildren after the court ruling on Senate Bill 1070 Guy Adams 'I can get my family back': immigrants driven out of Arizona return home The judge's decision is a setback however for Arizona's governor Jan Brewer Jill Torrance/Arizona Daily Star/AP

Mr Trump called the sheriff a "great American patriot" and claimed he had "done a lot in the fight against illegal immigration," in an interview with Fox News in August.

"Was Sheriff Joe convicted for doing his job?" he wondered at a campaign rally later that month.

The President's decision to pardon Mr Arpaio was condemned by many on the left and right – including Arizona's two Republican Senators, Mr Flake and John McCain. Mr Arpaio dismissed the Senators' comments on Tuesday, telling NBC News: "I don't have to talk to them."

The 85-year-old also played off concerns about his age, saying he only planned to serve one term.

"I’ll gun anybody," he told NBC. "What’s the age got to do with it?"