Roy, who received the party membership from state AAP functionaries here on Tuesday, said she expected the new party would bring about a qualitative change in politics.
"Most other parties have become outdated and cannot bring about a change. A change is essential and I expect AAP will strive for that," she said.
Mary Roy expects AAP would bring about a qualitative change in politics.
Roy successfully fought a prolonged legal battle for establishing inheritance right of Keralite Syrian Christian women over family properties.
She is also an educator and campaigner for women's rights and social justice. Last week, Malayalam novelist and campaigner Sara Joseph joined AAP.