Elliot was born in Portland, Oregon, to Fred and Clara Elliot. Fred was of Scottish heritage; his grandparents were the first of his family to settle in North America. Clara's parents moved near the turn of the 20th century from Switzerland to eastern Washington, where they operated a large ranch. They met in Portland, where Clara was studying to be a chiropractor and Fred, having devoted himself to Christian ministry, was working as a traveling preacher with the Plymouth Brethren church. After two years of correspondence, they were married in 1918. Robert, their first child, was born in 1921 while they were living in Seattle, and he was followed by Herbert, Jim, and Jane, all three of whom were born after the family moved to Portland. Elliot's parents had firm Christian beliefs, and they raised their children accordingly, taking them to church and reading the Bible regularly. Elliot professed faith in Jesus at the age of six and grew up in a home where obedience and honesty were enforced. The Elliot parents encouraged their children to be adventurous, and encouraged them to "live for Christ".
In 1941, Elliot entered Benson Polytechnic High School, studying architectural drawing. There he participated in numerous activities, including the school newspaper, the wrestling team, school plays, and the public-speaking club. His acting ability led some of the teachers in the school to suggest that he pursue acting as a career, and his oratorical skills were similarly lauded—after preparing and delivering a speech in honor of President Franklin D. Roosevelt hours after his death, a faculty member praised it.
Elliot used his speaking ability regularly. A classmate recounts how Elliot quoted the Bible to the president of the student body as an explanation for his refusal to attend a school party. Another time, Elliot risked expulsion from the public-speaking club by refusing to give a political speech, believing that Christians were not to