Former Pakistan Prime Minister Imran Khan has been given three-year jail sentence over corruption allegations.
A court in Islamabad found him guilty of not declaring money he had earned from selling state gifts. He denies the charges and says he will appeal.
After the verdict, Mr Khan was taken into custody from his home in Lahore.
The former cricketer, 70, was elected in 2018, but was ousted in a no-confidence vote last year after falling out with Pakistan's powerful military.
Mr Khan is facing more than 100 cases brought against him since his removal - charges he says are politically motivated.
Saturday's verdict centred on charges that he incorrectly declared details of presents from foreign dignitaries and proceeds from their alleged sale.
The gifts - reported to be worth more than 140 million Pakistani rupees ($635,000) - included Rolex watches, a ring and a pair of cuff links.
Mr Khan's barrister Gohar Khan said the verdict was "a murder of justice".
"We weren't even given a chance. We weren't even allowed to cross [examine], to say anything in defence or conduct our arguments. I haven't seen this kind of injustice before," he told Dawn newspaper.
As the court decision was announced, a crowd, which included some prosecuting lawyers, began chanting "Imran Khan is a thief" outside the building.
His party, Tehreek-e-Insaf, confirmed to the BBC that after being arrested in Lahore, Mr Khan was flown to the capital, Islamabad, to begin serving his sentence.
For months he had avoided arrest, with his supporters at times fighting pitched battles with police to keep him out of custody.
In May, Mr Khan was arrested for not appearing at court as requested. He was then released, with the arrest declared illegal.
Since then, his party has been under intense pressure from the authorities.
Many senior officials have left and thousands of supporters have been arrested, accused of being involved in the protests that followed Mr Khan's arrest.
Pakistan's army plays a prominent role in politics, sometimes seizing power in military coups, and, on other occasions, pulling levers behind the scenes.
Many analysts believe Mr Khan's election win in 2018 happened with the help of the military.
In opposition, he has been one of its most vocal critics, and analysts say the army's popularity has fallen.
Since being ousted, Mr Khan has been campaigning for early elections.
Conviction would disqualify Mr Khan from standing for office, possibly for life.
Pakistan's parliament will be dissolved on August 9, leaving a caretaker government to take over in the run up to the elections.
No election date has been announced, although constitutionally they should take place by early November.