She graduated with a degree in Classics and History from the University of King's College in Halifax, Nova Scotia, Canada.
O'Neil was first elected to the Maine House of Representatives in November 2016, succeeding fellow Democrat Justin Chenette.
[4] While serving in the Legislature, O'Neil earned her Juris Doctor degree from the University of Maine School of Law.
O'Neil received the Electronic Privacy Information Center (EPIC) 2024 Champion of Freedom Award for her work to safeguard the right to privacy, open government, and democratic values with courage and integrity.
[6] In December 2024, O'Neil revealed that she had been diagnosed with Acute Myeloid Leukemia and had begun chemotherapy.