The 35-year-old solicitor was accused of lying to police, as Labour withdraw the whip and call on her to resign.
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.
She was elected to the House of Commons in June 2017 with a majority of 600 votes and promoted to a whip - but stood down from the role last month.
A Labour spokesperson confirmed Onasanya was having the whip removed "with immediate effect" and said they were "deeply disappointed in" her behaviour.
"It falls well below what is expected of politicians and she should now resign," they added.
Onasanya will be sentenced alongside her brother on a date yet to be determined.
Festus, 34, from Cambridge, admitted perverting the course of justice three times to avoid speeding points.