The move places him atop the nation's top federal law enforcement agency despite doubts from Democrats about his qualifications and concerns he will do Donald Trump's bidding and go after the Republican president's adversaries.
"I cannot imagine a worse choice," Democratic senator Dick Durbin told colleagues before the 51-49 vote by the Republican-controlled Senate on Thursday.
Senators Susan Collins and Lisa Murkowski were the lone Republican holdouts.
A Trump loyalist and fierce critic of the agency, Patel will inherit an FBI gripped by turmoil as the Justice Department has forced out senior officials and demanded the names of thousands of agents who took part in investigations related to the January 6, 2021, riot at the US Capitol.
Patel has spoken of overhauling the FBI, including a renewed emphasis on the bureau's traditional crime-fighting duties rather than the intelligence-gathering and national security work.
But he also echoed Trump's desire for retribution, raising alarm among Democrats for saying he would "come after" anti-Trump "conspirators" in the federal government and the media.
Republicans angry over what they see as law enforcement bias against conservatives during the Democratic Biden administration, as well as criminal investigations into Trump, have rallied behind Patel.
"Mr Patel wants to make the FBI accountable once again - get back the reputation that the FBI has had historically for law enforcement," senator Chuck Grassley, chairman of the Senate judiciary committee, said before Patel was confirmed.
After his confirmation, Patel posted on social platform X that "the American people deserve an FBI that is transparent, accountable, and committed to justice", claiming the "politicalisation of our justice system has eroded public trust".
Democrats complained about Patel's lack of management experience and highlighted incendiary past statements they said called his judgment into question.
"I am absolutely sure of this one thing: this vote will haunt anyone who votes for him. They will rue the day they did it," senator Richard Blumenthal said, warning Patel would "completely and utterly disgrace this office and do such grave damage to our nation's justice system".
Patel's eyebrow-raising remarks on hundreds of podcasts and in other interviews in the past four years include referring to law enforcement officials who investigated Trump as "criminal gangsters", saying some January 6 rioters were "political prisoners", and proposing to shut down the FBI headquarters and turn it into a museum.
At his Senate hearing in January, Patel said Democrats were taking some of his comments out of context or misunderstanding the broader point that he was trying to make.
Patel has also denied that a list in a book he authored of government officials who he said were part of a "deep state" amounted to an "enemies list".
FBI directors are given 10-year terms as a way to insulate them from political influence.
Patel was selected in November to replace Christopher Wray, who was picked by Trump in 2017 but the president came to see as insufficiently loyal.
He resigned before Trump took office.
The FBI's interim leaders have clashed with the Justice Department over its demands for details about the agents who investigated the Capitol riot - a move that could lead to broader firings.
Patel, a former counterterrorism prosecutor, attracted Trump's attention in the president's first term when, as a House Republican staffer, Patel helped write a memo criticising the FBI's investigation into ties between Russia and Trump's 2016 campaign.
Patel later joined Trump's administration as a counterterrorism official and as chief of staff to the defence secretary.
21°C