Trimble was born in Mesa, Arizona in 1939. When he was eight, his family left the Salt River Valley and moved to Ash Fork, Arizona where is father worked for the Santa Fe Railroad. Following high school, Trimble enrolled at Phoenix College where he was a member of the nationally ranked baseball team. During those same years he played for the semi-pro Glendale Greys baseball team. The 1956 Greys were runner-up for the Arizona State Semi-pro Baseball Championship.

In February 1957 Trimble dropped out of college and joined the United States Marine Corps. Inspired by a Marine buddy, he purchased his first guitar in 1958 and taught himself to play while listening records by Johnny Cash, Elvis, and Buddy Holly. His motivation for leaning the guitar was to overcome shyness and to attract girls. He returned to college and graduated from Arizona State University in 1961. Two years later Trimble was touring with the Gin Mill Three, a folk group performing Kingston Trio-inspired music. During his travels he took the opportunity to visit a variety of historical sites and museums. While visiting the Little Big Horn Battlefield in Montana in 1968 Trimble made up his mind to become a western historian and writer. He returned to Arizona State University, taking every available course in Arizona and Western history. In 1969 he began teaching at Coronado High School.) Initially teaching American history, after two years he was teaching 10 sections of Southwest history. As part of his teaching style, he played his guitar and sang old Johnny Cash songs to demonstrate how folk music and history were interrelated.

In 1972, Trimble was asked to create an Arizona history class at Scottsdale Community College. Within three years it was one of the largest classes at the college and in 1977 began serving as director of that school's Southwest Studies program. After publishing his first book in 1977, he used his guitar and songs to liven up promotional book readings. Since then he has hosted several radio shows,including Trimble’s Tales and The Emmy award-winning television show, Arizona Backroads. Additionally he has appeared on CBS This Morning, Good Morning America, KAET-TV at ASU and the Nashville Network.He appears several times a year on stage at Prescott's Historic Palace Restaurant and Saloon on Whiskey Row.