Probably arose in early-20th-century Western fiction and movies where an employee or friend armed with a rifle or shotgun would ride next to a stagecoach driver for protection from bandits Indians.
- (idiomatic, slang) To ride in the front passenger seat of a vehicle, next to the driver. [from 1963]
- 1913, Alfred Henry Lewis, Faro Nell and Her Friends: Wolfville Stories:
- That's why, when the stage is stopped, the driver's never downed. Which if thar's money aboard, an' the express outfit wants it defended, they slams on some sport to ride shotgun that trip
- 2018 December 25, Austin Murphy, “I Used to Write for Sports Illustrated. Now I Deliver Packages for Amazon.”, in The Atlantic:
- Before sending me out alone, the company assigned me two “ride-alongs” with its top driver, the legendary Marco, who went out with 280 packages the second day I rode shotgun with him, took his full lunch break, did not roll through a single stop sign, and was finished by sundown.
- When both kids want to ride shotgun with Mom, they'll just have to take turns.
- (idiomatic, slang, figuratively) To accompany someone in order to assist and protect.
- He attended the meeting to ride shotgun for the sales team, in case anyone had a technical question.