Launched in March last year, the service was supposed to be completed by the end of the year but suffered delays.
Inaugurating the service, Sharif said that Pakistan was changing and those traveling in the modern buses will feel as if they were in another country.
"The project is a gift to the people of the Rawalpindi and Islamabad. We will also launch similar projects in other major cities," he said.
The 23-kilometre dedicated lane links the twin cities of Islamabad and Rawalpindi with help of 68 air-conditioned buses that would help about 135,000 commuters daily.
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Its 24 stations are decorated with glistening tiles, escalators, elevators and modern glass and steel structures with roofs. It is said to provide quality service at minimum cost of Rs 20 per person.
The project was marred by allegations of inflated cost and delays which irked travellers and provided fodder to opposition parties.
The brain behind the project is said to be Punjab Chief Minister and the premier's brother, Shahbaz Sharif, who has a penchant for mega projects.
The twin-city metro bus service is the second project after the first was opened by Shahbaz in Lahore in 2013, which has also been popular with commuters.