The Independent Office for Police Conduct (IOPC) found gross misconduct proven against PC Aaron Parry at a hearing organised by the force, which ended on July 8.
PC Parry was found to have breached professional standards of behaviour for authority, respect and courtesy; duties and responsibilities; orders and instructions; and discreditable conduct.
One video contained "inappropriate commentary" on the pandemic and another referred to a detained person as an "illegal immigrant".
Derrick Campbell, from the IOPC, said the officer "should have known better".
“Police forces have strict policies in place to ensure social media use is not abused by its officers,” he said.
“In the videos PC Parry identified himself as a police officer in uniform and in a police car, in violation of Northamptonshire Police’s social media policy.
“PC Parry claimed a lack of awareness of the relevant policies, but ignorance is no defence. He should have known better and, by coming to its decision, the independent panel has agreed.”
Mr Campbell said that PC Parry is “a person in a position of responsibility” and recording the images while on duty “negatively impacted on the public’s view of policing in general.”
The investigation began in May 2020 after a woman complained that inappropriate videos were posted on TikTok between January 19 2020 and April 8 2020.
The IOPC said the videos included one of PC Parry and a colleague who appeared in police uniform and which contained references to a detained person as an “illegal immigrant”.
In another, he and a colleague appeared in police uniform in a police vehicle and the video made inappropriate comments on the coronavirus pandemic.
A further video showed an unidentified man in the passenger seat of an Audi with the caption “drug dealer”.
Another officer, who has not been named, has received a written warning.
Supt Natalee Wignall, head of professional standards at Northamptonshire Police, said: "PC Parry, who up to this point had enjoyed a long and unblemished service record, expressed considerable remorse at the hearing."
She said PC Parry admitted, "his conduct was immature [but] he had never intended to cause offence to anyone".
"Since this case came to light, the force has taken further steps to educate officers around the use and misuse of social media and kept its social media policy under constant review," she added.