Senator Nancy King was born and raised in Niagara Falls, New York. She graduated from the Niagara Falls public school system and attended Niagara County Community College.

Upon moving to Maryland in 1981, King became involved in a number of civic organizations and in 1987 she became Vice-President and Chief Financial Officer of Trecor, Inc., a family-owned consulting and forensic engineering company, a position she held for over 25 years.

King's children attended Montgomery County public schools, and it was during that time that she began volunteering in the school system. In 1993, she became President of the Montgomery County Council of Parent-Teacher Associations (PTAs).

In 1994, King was elected to the Montgomery County Board of Education representing District 1 and quickly rose through the leadership ranks, and served for two years as President. Mrs. King continued to serve on the School Board until 2002, until she was elected to Maryland's House of Delegates representing District 39.

As a member of the House of Delegates, King served on the Ways and Means Committee where, in 2006, she became the Chair of the Education sub-committee. In August of 2007, King was elected by the Montgomery County Democratic Central Committee to fill the seat left vacant by the retirement of Senator P.J. Hogan. Subsequently, Governor Martin O'Malley approved the appointment and she was sworn in as Senator for District 39 on September 6, 2007. She subsequently won the general election and continues to serve District 39 in the Maryland Senate.

King has become an active leader in the Senate serving as the Senate Majority Leader and has been recognized by several organizations for her service including: State Legislator of the Year by the National Biotechnology Industry Organization; Technology Advocate of the Year by the Tech Council of Maryland; the Maryland Association of Boards of Education Charles W. Willis award; the Dental Association's Legislator of the Year award and the Dr. Nancy S. Grasmick Leadership Award in Early Care & Education. Additionally, in March of 2017 she was given the Senate of Maryland's First Citizen award for outstanding public service. Senator King serves on the Budget and Taxation Committee and the Capital subcommittee and serves as the Chair of the Education, Business and Administration subcommittee.