Avari, of Zoroastrian Parsi origin, was born Eruch Avari in Darjeeling, India, the great-grandson of Sir J. J. Madan, scion of the Madan family of Darjeeling. His father, also Eruch Avari ran a movie theatre and a guesthouse in Darjeeling. It was in this town in the Himalayan foothills that Avari spent his childhood. Avari has said that his family met the Dalai Lama during his childhood. His early education was at the prestigious North Point (the school division of the St. Joseph's College), which he attended as a "day-scholar".

Avari is known for his roles in films such as Stargate, Independence Day, The Mummy, Planet of the Apes and Mr. Deeds. Along with Alexis Cruz, he is one of only two actors to appear in both the original Stargate movie and the spin-off series Stargate SG-1. However before arriving in Los Angeles in 1991 his extensive work on stage has garnered him much praise from theater critics across America. Most notably as Vasquez, in 'Tis Pity She's a Whore with Val Kilmer at the Joseph Papp Public Theater and as Sir Richard at The Guthrie Theater's memorable production of "The Screens".

He has also made guest appearances on Law & Order, Star Trek: The Next Generation, Star Trek: Deep Space Nine, Star Trek: Enterprise, The X-Files, Babylon 5, Alias and The O.C.. He played cameo roles in JAG, Living People, NYPD Blue, Cheers, Murder, She Wrote, Judging Amy and NCIS. In the video game Zork Grand Inquisitor, he played Grand Inquisitor Mir Yannick, a ruthless dictator who serves as the game's main villain. He recently acted in The Librarian: Return to King Solomon's Mines.

Beginning in the fall of 2006, a photograph of Avari and a recording of his voice have been used in the role of Chandra Suresh in Heroes. The actor did not however appear on screen until the episode Seven Minutes to Midnight, as his character is one of the backstory and had died before the events of the pilot. When the character does appear it is only in flashbacks until Six Months Ago, when the story moves back to six months before the events of the pilot episode. In this episode, Suresh is seen as he moves to New York and contacts people on "the list" he generated of those he believes to have special genetic aberrations.

In the course of his career, Avari has portrayed representatives of more than 24 different nationalities. As of November 2006, Avari has appeared in 33 feature films and over 70 television episodes. Avari has appeared with Brent Spiner in three different productions: "Star Trek: The Next Generation" (1987), Independence Day (1996) and The Master of Disguise (2002).

Avari was scheduled to reappear in his role as Kasuf in the "Stargate SG-1" season six finale "Full Circle", but failed to do so due to his commitment to "Dragnet" (2003).