Her father, John Hennessy, was a meat salesman and sales/marketing executive, a job that required considerable travel and resulted in frequent moves for the family.

Her mother, Maxine, a secretary, left the family in 1982, leaving her daughter to be partially raised by her paternal grandmother, Eleanor, in Kitchener, Ontario.

[2] She attended Stanley Park Senior Public School and graduated from Grand River Collegiate Institute, both in Kitchener, Ontario,[3] and used to busk in the Toronto subway.

[4] Hennessy and her sister, Jacqueline, made their acting debut playing twin call girls in 1988's Dead Ringers.

Hennesey's big network breakthrough came in 1993, when Dick Wolf signed Hennessy as assistant district attorney Claire Kincaid in the NBC crime drama Law & Order.

That same year she appeared in a small role as Commander Mulcahy in the Steven Seagal action film Exit Wounds.

She also appeared as a veterinarian in the HBO series Luck, and promoted Zaxby's "Zalads" in a pair of television commercials in 2012.

They had a second marriage ceremony in January 2001, which took place at New York City Hall with Mayor Rudy Giuliani officiating.