“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.