A Charleston native, Hallanan was West Virginia's first female federal judge. She made history as the first woman to serve as a judge of a court of record and lead Kanawha County's first full-time juvenile court. Her appointment to the Public Service Commission in 1961 furthered her influence.

From 1983 to 1991, she served as a federal judge, notably reforming the state's child support program. After taking senior status in 1996, she continued in leadership roles with Columbia Gas System and Charleston National Bank.