Originally from Lake Forest, Illinois, McLennan attended the Hotchkiss School in Connecticut. In 1970, he received his BA degree (Magna Cum Laude and Phi Beta Kappa) from Yale University, where he was a member of the Wolf's Head Society. Along with former Yale Chaplain and McLennan's mentor William Sloane Coffin, McLennan was the inspiration for the Doonesbury cartoon character Reverend Scot Sloan in his college roommate Garry Trudeau's Pulitzer Prize-winning comic strip, which also was adapted into a film and nominated for an Academy Award for Best Animated Short Film.

His senior year at Yale, McLennan was chosen to be a "Scholar of the House", whereby he was exempt from attending class and allowed to focus the year on scholarly research. For his graduate education, he earned both Master of Divinity and Juris Doctor degrees cum laude from Harvard Divinity and Law School respectively in 1975.

He was ordained in 1975 as a Unitarian Universalist minister (and is a Unitarian Universalist Christian), and admitted to the Massachusetts bar in 1975. After practicing church-sponsored poverty law in a low-income region of Boston for nearly ten years and founding the Unitarian Universalist Legal Ministry, he was appointed University Chaplain at Tufts University in Massachusetts, serving from 1984 to 2000, and senior lecturer at Harvard Business School, serving from 1988 to 2000.

In addition to being the Dean for Religious Life at Stanford, he is a community minister at the Unitarian Universalist Church of Palo Alto.

In 1994, he was the recipient of The Rabbi Martin Katzenstein Award, the oldest annual award given to Harvard Divinity School Alumni "to honor among its graduates one who exhibits a passionate and helpful interest in the lives of other people."

McLennan was honored with the Gandhi, King, Ikeda Award in 2004.

 The award was "established to recognize leaders who promote peace and world reconciliation" by [[Morehouse College]].

McLennan's first book, Finding Your Religion: When the Faith You Grew Up With Has Lost Its Meaning, was published in 1999 by HarperSanFrancisco. His second book, Church on Sunday, Work on Monday: The Challenge of Fusing Christian Values with Business Life, was co-authored with Laura Nash and published in 2001 by Jossey-Bass. His third book, Jesus Was a Liberal: Reclaiming Christianity for All, was published by Palgrave-Macmillan on May 12, 2009.

In 2009, he went on a national book tour for Jesus Was a Liberal, presenting at more than a dozen book signings in Northern and Southern California, including a presentation for Authors@Googleat the company's Mountain View, CA headquarters. Other book events took place in Chicago, Minneapolis, Dallas, Greenwich, CT, Boston, New York City and Washington, D.C.

A prominent speaker on religion and ethics, McLennan has been featured in major news publications, such as USA Today,People Magazine,The Huffington Post,The Dallas Morning News,and The Boston Globe,as well as a guest on national and regional television and radio programs, including The CW Television Network,The O'Reilly Factor,National Public Radioand Sirius Satellite Radio.

Scotty McLennan is married to Ellen. They wed in 1981 in Boston, Massachusetts. They are the parents of two sons: Will McLennan (b. 1982) and Dan McLennan (b. 1984), both of whom are alumni of Stanford University.

From 1966-1967, McLennan played for the Yale Bulldogs men's ice hockey team.

He serves on the Board of Directors for the American Civil Liberties Union.

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