Wednesday's sentencing by an anti-graft court in Islamabad comes a day after Imran Khan, 71, was handed a 10-year jail term in another case in which he was convicted of revealing state secrets, and a week before national elections.
In August last year the former cricket superstar was also handed a three-year prison sentence by another court for selling gifts worth more than 140 million rupees ($NZ819,000) in state possession and received during his 2018-2022 premiership.
The sentence was later suspended but Khan remains behind bars in connection with other cases. He has said that he legally purchased the items.
Government officials have alleged Khan's aides sold the gifts in Dubai.
On Tuesday, a special court found Khan guilty of making public the contents of a secret cable sent by Pakistan's ambassador in Washington to the government in Islamabad, his Pakistan Tehreek-e-Insaf (PTI) party said.
Former foreign minister Shah Mehmood Qureshi was also sentenced to 10 years in the same case.
The court is likely to issue a written verdict within a day or two. Khan's PTI party said it would challenge the ruling.
"We don't accept this illegal decision," Khan's lawyer, Naeem Panjutha, posted on social media platform X.
The PTI has not called for protests or demonstrations before the election. A bomb in Pakistan's Balochistan region killed three PTI members on Tuesday, the party said, hours after Khan was sentenced. There were no details of who was responsible.
Khan aide Zulfikar Bukhari told Reuters that the legal team was given no chance to represent Khan or cross-examine witnesses. The proceedings were carried out in maximum security Adiala jail in Rawalpindi.
Another of Khan's lawyers, Ali Zafar, told ARY television that given the circumstances of the trial and sentencing, the chances of the case being quashed on appeal were "100%".
Bukhari called the conviction an attempt to weaken support for Khan. "People will now make sure they come out and vote in larger numbers," he told Reuters.
The party of three-time Prime Minister Nawaz Sharif, Khan's main political opponent, said the verdict was not harsh enough.
"I think, based on his carelessness and crime - pertaining to important national interests - this is a very light sentence," Ahsan Iqbal, a senior Sharif aide, said in a TV interview.
MULTIPLE CASES
Analysts believe Sharif's party is the frontrunner to form the next government. Sharif and his daughter, Maryam Nawaz, were convicted and jailed over graft allegations days before the last general election in 2018. Analysts say that that helped Khan win, while Khan's sentence now helps Sharif. Both blame the military.
Khan's sentencing just before the polls will "raise questions about the election's credibility", said Mazhar Abbas, a Karachi-based analyst.
Pakistan's recovery from an economic crisis depends on political stability. The election comes as Pakistan is navigating a tricky recovery path under a $US3 billion International Monetary Fund bailout that helped it narrowly avert a sovereign default last year.
Khan has been fighting dozens of cases since he was ousted from power in a parliamentary vote of no-confidence in 2022. He says the secret cable mentioned in the case was proof of a conspiracy by the Pakistani military and the US government to topple his government in 2022 after he visited Moscow, just before Russia's invasion of Ukraine.
Washington and the Pakistan military deny the accusations.
Khan has previously said the contents of the cable appeared in the media from other sources.
Khan's PTI suffered a major setback this month when a court upheld the Election Commission's decision to strip the party of its traditional election symbol, the cricket bat.
His candidates are now contesting as independents, many of them on the run amid what the party calls a crackdown backed by the military. The military denies this.
Khan's media team posted a message from the jailed leader on X ahead of the verdict.
"These people want to provoke you by giving me a harsh sentence in this case so that you go out on the streets and protest, then add unknown people to the crowd and then do another false flag operation," the post said.
In May last year, the first time Khan was arrested, his supporters were accused of rioting, and hundreds were arrested and tried. Khan denies his supporters were part of the mob.
Many of them have faced arrest while attending subsequent party rallies or demonstrations.
Khan urged his supporters to vote for candidates backed by him. "This is your war and this is your test that you have to take revenge for every injustice by your vote on February 8 while remaining peaceful," the post on X said.
