Imran Khan, the former cricket star turned firebrand politician, was sworn in as Pakistan’s prime minister on Saturday, taking control of a country facing a looming economic crisis as observers questioned whether he had the political acumen to govern a deeply divided nation.

Mr. Khan’s first decision was to scrub the nine-course meal traditionally served after the oath-taking ceremony, held at the president’s house. It was a sign of the “austerity drive” he had promised while on the campaign trail, his party said. Instead, refreshments were served in the grand hall of the residence.

Since winning the July 25 election, Mr. Khan has stressed that he would lead a lean life, shunning the ostentatious displays of power and wealth of his predecessors. He has said that he will not live in the prime minister’s house, a lavish, white marble building on a hilltop overlooking Islamabad.

Instead, he vowed to take a smaller house belonging to the military secretary. Mr. Khan, however, maintains a sprawling, private Mediterranean-style villa nearby.