Kenneth Earl Tilsen was born on 4 November 1927 in New Leipzig, North Dakota, one of five children in the family. Tilsen's family lived briefly in Michigan, then moved to St. Paul, Minnesota when Tilsen was in the first grade.
Tilsen's awareness of social inequities and the disenfranchised began early in life. Tilsen's father founded Tilsen Homes, the Twin Cities' first builder of integrated housing. Tilsen spent his formative years in St. Paul's Selby-Dale neighborhood, at the time the most integrated in the Twin Cities and later attended integrated Marshall High School. After serving briefly in the navy, Tilsen went on to the University of Minnesota where he completed law school, graduating at the top of his class in 1950.
Tilsen began his legal career with the firm of Robbins, Davis & Lyons where he practiced for fourteen years before becoming an independent practitioner. Throughout his life Tilsen has been an active supporter of what he described as "political and social movements for change." Areas of particular interest during his legal career included draft resistance, civil rights, student protests, and other issues relating to social activism.
In 1964 Tilsen was investigated by the House Committee on un-American Activities for alleged activities as president of a Marxist-Socialist club during 1948-1950 at the University of Minnesota. He made news headlines when he staunchly refused to answer the committee's questions regarding activities before September 1950, when the Internal Security and Subversive Activities Control Acts were passed, giving the committee its authority. After successfully thwarting the committee's attack on himself, Tilsen became known as a "protest" attorney, taking public interest cases, often pro bono, and defending other "anti-establishment" protesters, such as members of the Honeywell Project and the students involved in the 1969 takeover of the University of Minnesota's Morrill Hall.
Tilsen also represented members of the famed "Minnesota Eight" accused of a 1970 draft office break-in. Following the 71-day Indian occupation of the village of Wounded Knee (S.D.) in 1973, Tilsen gained national prominence as chief legal coordinator for the Wounded Knee Legal Defense/Offense Committee and attorney for American Indian Movement leaders Dennis Banks and Russell Means.
In 1947 Tilsen married Rachel Le Sueur, daughter of Minnesota writer, feminist, and activist Meridel Le Sueur. The two had met earlier that year at St. Paul's Prom Ballroom at a protest over its policy not to admit blacks. The couple had five children. Following his retirement from legal practice in 1993, Tilsen joined the faculty at Hamline University Law School, specializing in teaching litigation skills and running a clinic through which students learned to handle public interest lawsuits.