McCain also lashed out at Mulvaney's efforts on military affairs, including a vote in 2011 that the Arizona senator said would have brought the immediate withdrawal of all USA troops from Afghanistan, ending a mission to prevent it from "becoming a safe haven for terrorists".
The South Carolina Republican was narrowly confirmed in a 51-49 vote.
McCain said he generally gives deference and "the benefit of the doubt" to incoming presidents of both parties when it comes to their Cabinets and that "it is with great reluctance" that he is coming out against Mulvaney. Mick Mulvaney as the new director of the Office of Management and Budget Thursday morning, allowing the budget process to move forward.
Immediately after the confirmation of Mulvaney, the Senate will turn to EPA nominee Scott Pruitt, the staunchly conservative Oklahoma attorney general.
House Speaker Paul Ryan, R-Wis., said Mulvaney will "improve the way government does the people's business".
Trump has said that strengthening the military is more important than balancing the budget and is committed to ending budget caps.
Man accuses Justin Bieber of assault, theft
Caroline McBride, director of public relations for Serafina Restaurant Group, denies that any staff member was involved. The man says Bieber's crew also got involved and that he ended up with a concussion and other injuries.
KL Hospital finishes post-mortem on North Korean
According to the MPs, Kim had been given China's protection and was due to leave for Macau when he was killed by the agents. He told medical workers before he died that he had been attacked with a chemical spray , the Malaysian officials said.
European Union Parliament OKs free trade deal with Canada
But US President Donald Trump as part of his election pledge ordered the withdrawal from TPP and renegotiation of NAFTA. The deal was finally signed in Brussels last October with Canadian Prime Minister Justin Trudeau present.
President Donald Trump's choice to run the White House budget office has cleared a routine Senate hurdle.
Senator John McCain (R-AZ) speaks to reporters as he arrives for the Republican policy luncheon on Capitol Hill in Washington, U.S., February 14, 2017.
Boccia said she is confident that Mulvaney will work to reform entitlement programs and address government spending.
"In my view, out of control mandatory spending must be addressed to solve our nation's fiscal problems".