Maryam, considered the heir apparent of Sharif, also received a 7-year sentence with a 2-million-pound fine ($2.6 million), while her husband Captain (retd) Safdar was sentenced to one year. Sharif and his daughter are in London, where Sharif's wife Begum Kulsoom is undergoing treatment.
"We will use all legal and constitutional options against today's court rulings", said Shahbaz Sharif, the party chief, appealing on supporters to exercise restraint and vote for their candidates in the July 25 vote.
Pakistan's Supreme Court in July 2017 disqualified Nawaz Sharif over long-running corruption allegations against him and his family, a move that saw Sharif tender his resignation-triggering political turmoil and putting a question mark over Pakistan's commitment to democracy.
With the conviction of both Maryam Nawaz and Capt Safdar in the case, they stand debarred from contesting the upcoming Parliamentary elections in Pakistan which will dampen the hopes of PMLN which was planning to make a comeback to power.
The agency had also named Sharif's sons - Hussain Nawaz and Hassan Nawaz - as accused in the three cases.
"This decision is based on injustice".
The verdict in the Avenfield reference case was read out by accountability court Judge Mohammad Bashir after postponing the announcement four times in a day.
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The new policy would not have the force of law, but it amounts to the official view of the federal government. Whether that happens and how that happens and who is on the court are all good questions.
Sharif was disqualified from office a year ago by the Pakistan Supreme Court, which declared him "dishonest" for not disclosing a separate monthly income from a company owned by his son.
But he has kept control of the Pakistan Muslim League-Nawaz (PML-N) party that he founded.
The decision comes at a time of growing suspicion of military meddling in politics ahead of the polls, as well as media complaints of being muzzled.
Sharif has previously described the court proceedings against him as politically motivated and a judicial witchhunt.
"Standing up to hidden powers who have ruled the country for nearly 70 years!"
He fell out with powerful generals once he ascended to power a decade later, and relations became fraught after his return as premier in 2013, partly because he challenged the military over foreign policy, which the generals traditionally considered their domain.
"PML-N's lions, remember this!"