The Millionaire's Wife is the story of Louisa Ignacio, a hardworking single mother and her crucial decision to settle in a marriage for convenience with an older man. She vows to be a loyal and dutiful wife to him in exchange of all the help he is giving her son who has juvenile diabetes.

After she agrees to marry Fred, a widower and one of the richest businessmen in the country, Louisa must now face the subsequent consequences of her decision which involves her stepdaughter, her stepdaughter's children, her love child, and her love child's father.

Will she be able to fulfill her vows to Fred? Will the plans of Stella, Jared, and Allison in ruining Louisa's life be successful? How far will Ivan go to win back Louisa, especially after he finds out that they have a child?