The 35-year-old solicitor was accused of colluding with her brother Festus after her car was clocked going 41mph in a 30mph zone in the village of Thorney, near Peterborough, in July last year.
The MP for Peterborough, who was elected in June 2017 but stood down as a Labour whip last month, was found guilty of one count of perverting the course of justice at the conclusion of the retrial on Wednesday.
Prosecutor David Jeremy QC told the jury she went on to lie “persistently and deliberately” to avoid prosecution.
She was “administratively suspended” by her party following the verdict. A Labour spokesperson said: “Labour Party is deeply disappointed in Fiona Onasaya’s behaviour. It falls well below what is expected of politicians. She should now resign.
“Fiona Onasanya is being administratively suspended from the Labour Party and therefore the whip with immediate effect.”
Her brother, 34, from Cambridge, admitted perverting the course of justice three times to avoid speeding points. The siblings face possible jail time when they are sentenced at the Old Bailey by Judge Nicholas Hilliard QC at a later date.
The court heard how Ms Onasanya’s Nissan Micra was caught speeding just after 10pm on 24 July 2017.
Ms Onasanya was sent a Notice of Intended Prosecution (NIP) that asked her to provide the name of the driver of the Micra at the time.
It was sent back naming Aleks Antipow, an acquaintance of her brother Festus. Authorities were unable to track down Mr Antipow at a false address provided on the NIP form, and he was later found to be out of the country at the time the offence took place.
Ms Onasanya claimed she left the NIP form at her mother Paulina Scott’s Cambridge home for whoever had borrowed her car to complete.
While being pursued over the NIP, the MP said she had been admitted to hospital for three days last September, having suffered a relapse of multiple sclerosis.
She said: “I was told I had a relapse and they had found more lesions on my brain. I probably was not in the best head space. I’ve just been told I had got an incurable degenerative disease. I think that would preoccupy anyone.”
The MP’s former communications manager Christian DeFeo came forward to provide evidence, placing her at his house in Thorney on the evening of 24 July.
Mr DeFeo told jurors he never imagined in his “darkest dreams” that he would give evidence against the woman who he helped get elected last June.
The Labour politician said she did not recall visiting Mr DeFeo’s house on 24 July, but could not rule out being behind the wheel of the car.
Donna Rayner, of the Crown Prosecution Service, said: “Fiona Onasanya and her brother Festus both lied to the authorities in the hope they could avoid the consequences of their speeding offences.
“Fiona Onsanya denied perverting the course of justice but the CPS presented evidence that her phone was in the area when the speeding took place and the man she had nominated as the driver was, in fact, out of the country. Clearly the jury did not believe her explanation.”
Additional reporting by Press Association