Sinéad was born in Kanturk in north Cork and is one of five children. When she was 8 years old, her parents fostered a young girl with an intellectual disability from the north inner city of Cork who came to live with her family. This opened her eyes to a new world which struck Sinéad as unfair, that disabled people and their families were generally seen as unequal, with pity, and completely lacking in support and opportunities, purely based on their social and economic background and where they happened to live.

She attended Midleton College and went on to study languages at Dublin City University. She became involved in the Fianna Fáil cumann there where she would make lifelong friends and become encouraged to be politically active. She began working as a translator living in London where she met her husband Darran, from Donegal, and eventually moved back to Ireland where she began a stellar career in the tech sector based in Dublin.