|U.S. House, Montana|
Rankin was born in Billings, Montana and graduated from Billings West High School in 1963. He then pursued his bachelor's degree in liberal arts with a major in Biology from Eastern Montana College (now Montana State University at Billings). In 1966, he joined the Peace Corps and taught public health and nutrition in India. He was drafted into the U.S. Army in 1968 and served over 8 months in Vietnam. After an honorable discharge, Rankin worked for several real estate companies in Billings before started his own firm, First Choice Real Estate, in 1983. He has taught biology on a contract basis for teachers on sabbatical at Montana public schools. 
Rankin ran in the 2012 election for the U.S. House, representing Montana's at-large House seat. He faced Kim Gillan, Diane Smith, Dave Strohmaier, Rob Stutz, Franke Wilmer and Jason Ward in the Democratic primary. Rankin was defeated by Kim Gillan in the Democratic primary on June 5, 2012.
Sam married in 1973 and divorced in 1977 and has a son from that marriage. Sam married Diane Williams of Billings in 1983 and they have two daughters.