He was born on 18 August 1932 at Sindhri in Tharparkar of Sindh. He was born to a family of agricultural landowners, and as a result he went toHastings, England, to study at the agricultural institute.
Junejo’s political career began shortly after graduating, when he was elected to Sanghar District council. He became a member of the Pakistan Muslim League and was then elected to the West Pakistan Provincial Assembly. Under Ayub Khan, Junejo served as the Minister for West Pakistan railways.
In 1977 Muhammad Zia-ul-Haq declared martial law, while Junejo served in a series of minor government posts. Following the 1985 elections, in which candidates were unable to represent a political party, Zia appointed Junejo as his Prime Minister. Zia assumed that Junejo would provide little opposition to Zia’s programme; however Junejo began his term by pushing for the end of marial law and the re-introduction of political parties. Zia ended martial law in December 1985, less than a year after Junejo’s appointment.
It was shortly after the re-introduction of political parties that Junejo formed the element of the Pakistan Muslim League that became PML-J, following his death.
Zia dismissed the Junejo government in 1988, following an investigation into the Ojhri Camp disaster, and its decision to sign the Geneva Accords on Afghanistan.
Junejo lost his government seat in the 1988 elections. He was elected to the National Assembly in 1990 and remained head of the PML. He held these posts until his death three years later.