Over his career, Daniel Sheehan has participated in numerous legal cases of public interest, including the Pentagon Papers case, the Watergate Break-In case, the Silkwood case, the Greensboro massacre case, the La Penca bombing case and others.
He established the Christic Institute and the Romero Institute, two non-profit public policy centers.
Sheehan has spoken publicly about UFOs/alien visitation and has participated in Disclosure Project events.
He represents Luis Elizondo, the former director of the Advanced Aerospace Threat Identification Program in a case against the US Department of Defense.
Since 2015 Sheehan has lectured on American history, politics and the assassination of John F.
Kennedy at the University of California, Santa Cruz.
Sheehan is currently Chief Counsel of the Romero Institute, where his focus is the Lakota People's Law Project.
Sheehan and The Lakota People's Law Project participated in legal cases related to the Dakota Access Pipeline protests.
In 2013 Sheehan published Daniel Sheehan: The People's Advocate, a memoir, through Counterpoint Publishing.