ISLAMABAD, Pakistan — With his term as Pakistan’s prime minister cut short, and with his governing party facing critical national elections in less than a year, Nawaz Sharif announced publicly on Saturday that he was choosing his younger brother, Shehbaz Sharif, to be his long-term replacement as prime minister and as the party’s standard bearer.

On one level, it was a clear choice. Over the past four years, as chief minister of Punjab Province, Pakistan’s most crucial political power base, Shehbaz Sharif, 65, has presided over a high-profile campaign of infrastructure improvements and social development programs.

“After losing out on the legal front, Nawaz Sharif cannot afford to also compromise on the integrity of his party,” said Rana Jawad, the news director of Pakistan’s most popular news channel, Geo News. “Shehbaz is an obvious choice to keep both the party united and carry brand Sharif forward.”

Where his older brother has been criticized in recent years for a low-energy style in power, Shehbaz Sharif has nurtured a nearly opposite reputation.

He has become known for surprise inspection “raids” of hospitals or schools, even in Punjab’s smaller towns, and his aides describe him as a workaholic with a taste for 7 a.m. staff meetings. Even his socks are vibrant — he will wear colorfully striped socks even when formally dressed.

But the choice is not without risk for the Sharifs’ party, the Pakistan Muslim League.

Though he is seen as popular, Shehbaz Sharif has also been dogged by accusations of police brutality under his watch as Punjab’s chief minister. And he has been criticized for doing too little to curb extremist sectarian groups in the province.

There are long-term questions about his health, as well. Over the years, Shehbaz Sharif has undergone multiple treatments for cancer, including of the spinal cord.

His supporters insist that the hard-nosed style he was known for in early years has softened somewhat. And advisers say that his medical challenges over the years have driven his recent campaign of social development.

In a statement to The New York Times on Friday night, before his selection was publicly confirmed, Mr. Sharif acknowledged that he would be taking the reins at a critical and turbulent time.

“I will accept what is best for the country and the party,” he said. “Pakistan has to move forward no matter how great the obstacles in our path.”

His path to the prime minister’s residence in Islamabad will not be instant. Over the next 45 days, another P.M.L. figure — the current petroleum minister, Shahid Khaqan Abbasi — will take over as interim prime minister. Shehbaz Sharif must step down as chief minister and win election to his brother’s seat in the National Assembly in a spot election, expected in the coming weeks, before taking over as prime minister.

That initial victory is nearly assured, given the party’s firm grasp on Punjab politics. But in the coming year, the Sharifs’ rivals, and in particular the former cricket star and political opposition leader Imran Khan, will seek to shake the P.M.L.’s dominance in Punjab.

Because of that, some see Shehbaz Sharif’s ascent to the prime minister post as being a bit of a gamble. At a time when Punjab politics will be the focus of fierce contest ahead of the 2018 national elections, taking the province’s political kingpin out of the day-to-day management of the campaign and public affairs there is not an automatic choice.

“Shehbaz Sharif has a proven record of carrying out mega-development projects in Punjab and delivering what the common man wants. Then why would you want to remove him from there?” said Nusrat Javed, a journalist and longtime observer of Punjab politics.

In the glare of the coming national political race, Shehbaz Sharif will also face tough scrutiny of his business dealings — often wrapped up with his brother’s — and about accusations of security abuses during his three separate terms as Punjab chief minister.

In 2014, at least seven people were killed in Lahore, Punjab’s capital city, in violent clashes between the police and followers of Muhammad Tahir-ul-Qadri, a fiery cleric who had called for mass anticorruption protests against Nawaz Sharif’s government. Shehbaz Sharif was accused of ordering the police to open fire, though he called a judicial inquiry after the killings.

And back in 2003, a court issued an arrest warrant for Mr. Sharif for having ordered the extrajudicial killings of five people in a staged police encounter in 1998, during his first tenure as chief minister. He was barred from contesting the 2008 election because of lingering murder charges in the case, which have since been dropped.

He is also accused of allowing banned sectarian organizations like Lashkar-e-Jhangvi to thrive in Punjab. More recently, though, the authorities’ killing in July 2015 of that group’s leader, Malik Ishaq, and some other militant commanders has been seen as an important shift in Mr. Sharif’s policy toward militants in his province.

Shehbaz Sharif is also seen as carrying one important advantage over his older brother. Where Nawaz Sharif, whose second term was cut short by a military coup in 1998, has always been feuding with the country’s domineering military establishment, Shehbaz Sharif is considered to have better relations with the generals. At moments of crisis, his aides say, he has sometimes been able to serve as a bridge between the military and his brother’s government.

But in other ways, there is still the potential for conflict with the military under a Shehbaz Sharif government. Like his brother, Mr. Sharif has been particularly vocal about his desire to improve relations with archrival India, a move that is anathema to the army.

And there is also the matter of his business dealings.

Shehbaz Sharif has so far been unscathed by the disclosures in the Panama Papers document leak that led Pakistan’s Supreme Court on Friday to disqualify his brother and order criminal investigations of other family members. But in the court’s same verdict, the justices also included an order to reopen a 2000 case into the Sharifs’ Hudaibiya Paper Mills company, which has been accused of serving in part as a money-laundering front for both Sharif brothers.

As with the Panama Papers accusations, the Sharifs’ main rival, Imran Khan, has been seen as driving public clamor to reopen that case.

“They should at least read the court’s full judgment before they decide to nominate Shehbaz,” said Fawad Chaudhry, a spokesman for Mr. Khan’s Pakistan Tehreek-i-Insaf Party.