The (now independent) Member of Parliament for Peterborough was found guilty of perverting the court of justice following a retrial in December.
The Old Bailey heard evidence the MP was texting as well as speeding on the evening of Monday 24th July last year, during the summer recess.
The 35-year-old solicitor was clocked going 41mph in a 30mph zone in the village of Thorney near Peterborough.
The prosecution alleged she went on to collude with her brother Festus to avoid a speeding ticket.
The court was told she was sent a Notice of Intended Prosecution (NIP) to fill out, but it was sent back naming the driver as Aleks Antipow, an acquaintance of Festus, who was away visiting his parents in Russia.
Festus, 34, from Cambridge, pleaded guilty to three counts of perverting the course of justice over speeding, including for the July 24 incident.
The siblings will be sentenced at the Old Bailey by Mr Justice Stuart-Smith on Tuesday.
In the wake of the guilty verdict, Onasanya was expelled from the Labour Party and has launched an appeal against her conviction.
If she is sentenced for a year or more, she will automatically lose her seat and if the sentence is less than a year then she could face a recall petition - where her constituency could recall her from parliament and trigger a by-election if 10 per cent electorate sign the petition.
A by-election could be a close and unwelcome match for Labour as she only won the seat in 2017 by 607 votes against the Conservatives with the area voting 60.9% Leave in the EU referendum.
The recall petition rules state however: "In the case of a conviction, the recall petition will not be opened unless the appeal period expires without the conviction, sentence or order having been overturned or all appeals have been heard and dismissed."
But if the sentence is less than that a recall petition can force a by-election if it is signed by more than 10% of the electorate in the Cambridgeshire seat.
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