Ma won the Democratic nomination to represent California's 19th Assembly District against fellow Democrat Janet Reilly in the state primary election of June 6, 2006.
The campaign was one of the more expensive legislative primary races in the state of California.
As a Supervisor, she also started her advocacy regarding banning toxins from children's toys - passing Ordinance Number 060107 to "prohibit the manufacture, sale, or distribution in commerce of any toy or child-care article…if it contains bisphenol-A or other specified chemicals." Fiona Ma was first elected to represent California’s 12th Assembly District from November 2006 to November 2012 (serving the maximum three terms).
She was the 112th woman to be elected to the California legislature and the first Asian woman to serve as Speaker pro Tempore since 1850.
Growing up, she was known as a tomboy, interested in sports, Girl Scouts, and academics. William Ma, was a civil engineer who later specialized in construction claims and litigation before he retired.