Clemenson was born and raised in Humboldt, Iowa, the son of drug store owners Ruth Alzora (Dayton) and Ernest Arnold Clemenson. In his early teens, he delivered the Des Moines Register, which had a long tradition of awarding scholarships to top east-coast preparatory schools to a select few "paper boys". Clemenson, a straight-A junior high school student, won a Register scholarship to Phillips Academy in Andover, Massachusetts. In 1973, while Chris was enrolled at Phillips Academy, his father died at age 58. He participated in many theatrical productions at Phillips Academy.
Upon graduation from Phillips in 1976, he entered Harvard College. From his freshman year onward he received important roles in campus stage productions, often receiving more praise from critics than the productions received. When Clemenson starred in aHarvard Lampoon sketch comedy show, a Harvard Crimson theatre critic panned the show but described Clemenson as "hugely talented actor who can trigger hysteria with any of a dozen subtle expressions or inflections."
Other Crimson critics described his performances in Shakespeare plays as "a tour de force of sheer talent and intelligence" (in The Winter's Tale) and "a very fine and subtle performance" (in Measure for Measure). He displayed early on his remarkable range when he undertook with inimitable flair and hilarious effect the hugely solemn role of Erde "the green-faced torso", goddess of the Earth, in Peter Sellers's Loeb Drama Center production of "Wagner's Ring".
During many summers he would return to Humboldt to star in, and later direct, local community theatre plays at Humboldt's Castle Theatre. After graduating from Harvard College in 1980 and the Yale School of Drama in 1984, he moved to Los Angeles. Clemenson and fellow Boston Legal star James Spader are old friends from Phillips Academy days.
Many of Clemenson's early roles in television and film matched his personality as a bright, soft-spoken professional. He was a law student in the television version of The Paper Chase, Alex Keaton's English teacher in the television show Family Ties, the bailiff in the Ivan Reitman movie Legal Eagles, the flight surgeon in the movie Apollo 13, a cop in The Big Lebowski, a killer in The Fisher King and Dr. Dale Lawrence in the movie And the Band Played On. While he has been a familiar face for over a decade, until recently his name was not so well known.
In 1999, Clemenson appeared in the Buffy the Vampire Slayer episode "Bad Girls" as a morbidly obese demon named Balthazar. He wore a large padded suit and extensive make-up for the role, and the character's repulsive, villainous nature contradicted many of his earlier roles.
Recently, Clemenson has become known for his role as Jerry "Hands" Espenson on the television series Boston Legal. For playing Espenson, he won an Emmy Award for Best Guest Actor in a Drama Series in 2006 and was nominated for the same award in 2007. He remained with the series through to its finale in 2008.
In film, he starred as real-life 9/11 victim Tom Burnett in United 93. On television, he was a regular on The Adventures of Brisco County, Jr. playing the part of Socrates Poole. He also had a recurring role on Veronica Mars as Abel Koontz. In total, Clemenson appeared in three episodes of the show: "Like a Virgin", "Mars vs. Mars", and "Rat Saw God". Clemenson also has appeared in a season 6 episode of NCIS, "Dead Reckoning". He also appeared in two season 2 episodes of The Mentalist. He also played Jimmy Masterson on the 3rd episode of Memphis Beat, "Love Me Tender."
In 2009, Clemenson joined CSI: Miami as the new medical examiner, Dr. Tom Loman as recurring cast member from 2009 to 2012, before canceling the show. He appeared throughout the show's eighth, ninth and tenth seasons as a recurring character. 2013, also he appeared as guest star in the NBC's short-lived series Harry's Law.