The 35-year-old solicitor and MP for Peterborough is now facing a misconduct tribunal over her conviction for perverting the course of justice.
On Friday, the Solicitors Regulation Authority (SRA) announced a decision to prosecute Ms Onasanya.
It found there was a "case to answer" over her conviction on 19th December last year.
It is alleged she failed to "uphold the proper administration of justice", "act with integrity" or "behave in a way that maintains the trust the public places in her and the provision of legal services".
The case will be brought before the Solicitors Disciplinary Tribunal and are "as yet unproven", the SRA said in a statement on its website.
At the full hearing, the SRA as the prosecuting authority, is expected to present its case to a Tribunal panel of two solicitors and a lay member, during which Ms Onasanya can challenge evidence or offer mitigation.
No date has yet been set for a hearing in central London but if the allegations are proved, Ms Onasanya could be fined, suspended from working as a solicitor or struck off.
Ms Onasanya was elected for Labour in the Cambridgeshire city in 2017 by a small majority of 607 votes.
What would you do if you knew you were innocent? In every single story, like a coin, there are two sides - now I am not legally restrained - this is mine.
— Fiona Onasanya (@FionaOnasanyaMP) March 18, 2019
Full video: https://t.co/ToyntFJ9W7 pic.twitter.com/yz6OV4HHhV
Within months of taking her seat, she colluded with her brother Festus after her car was clocked speeding at 41mph in a 30mph zone in the village of Thorney, near Peterborough, her Old Bailey trial was told.
She was sent a notice of intended prosecution to fill out, but it was sent back naming the guilty driver as Aleks Antipow, an acquaintance of her brother, who was away visiting his parents in Russia.
Pictured, right: Fiona Onasanya leaving prison earlier this year
Festus Onasanya, 34, from Cambridge, was jailed for ten months after he admitted three counts of perverting the course of justice over speeding.
Ms Onasanya, who lost an appeal against conviction, served 28 days of a three-month prison sentence and continued to sit as an MP and receive her £77,379 salary, despite being expelled from the Labour Party.
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