Arnold Olsen was born in Butte, Montana, to Norwegian immigrants. He graduated from Montana State University Law School and opened a private law practice in 1940. Olsen served in the Navy during World War II and later became the Attorney General of Montana, a position he held for two terms. He transitioned to federal politics, serving multiple terms in the U.S. House of Representatives before returning to state judicial roles, where he was elected and re-elected to the Second Judicial District of Montana. Throughout his career, Olsen demonstrated a commitment to public service and legislative work.

Arnold Olsen's political identity is marked by a blend of fiscal conservatism and progressive social policies, creating a unique ideological tension. He consistently advocated for balanced budgets and fiscal responsibility while simultaneously pushing for increased funding in public education and infrastructure. Olsen's environmental policies reveal a surprising commitment to sustainable resource management and conservation, often aligning with progressive factions. His stance on social issues, including civil rights and healthcare reforms, further underscores his progressive leanings, even as he served in more traditionally conservative roles. Olsen's approach to military and defense issues, rooted in his own service, consistently supported veteran benefits, revealing a nuanced perspective on national security.