The former international cricket star had long warned he would be arrested to prevent him from participating in elections due to be held before the end of the year.
Anyone convicted of a criminal offence is usually disqualified from contesting elections or holding office in Pakistan.
Khan, 70, has faced a slew of court cases for charges he has said are politically motivated since being removed from power in a vote of no confidence last year, and he was not present when he was sentenced on Saturday.
In May, he was arrested and briefly detained in Islamabad for the same case, sparking deadly unrest during which supporters of his Pakistan Tehreek-e-Insaf (PTI) party poured onto the streets and clashed with police.
In the aftermath of his release following three days in custody, PTI was targeted by a crackdown with thousands of arrests, reports of intimidation and muzzling of the media.
Images of Khan, or even mentions of him by name, are prohibited from being broadcast on TV channels, but he remains wildly popular, and last month a debut video to his personal TikTok account racked up more than 135 million views and 4.5 million likes within 36 hours.
After he was taken away by police on Saturday, a video statement Khan made before his arrest was posted to his X, formerly Twitter, account, with him calling for his supporters to protest.
“My fellow Pakistanis, they will have arrested me and I’ll be in jail by the time this message reaches you. I have just one request and appeal, that you are not to sit silently at home,” he said.
“This is a war for justice, for your rights, for your freedom … chains don’t just fall off, they have to be broken. You must continue peaceful protest until you get your rights.”
Khan’s jailing will do little to calm the economic and political unrest that has roiled the nation for the past 18 months.