The sudden death of the 31-year old Canadian actor came several months after he had voluntarily checked himself into a treatment facility for substance addiction.
Vancouver Police Department Acting Chief Doug LePard said at a televised news conference late Saturday "all indications are that there was no foul play." He also said that "the cause of death wasn't immediately apparent."
Monteith was discovered shortly after noon in a room at the Fairmont Pacific Rim Hotel in downtown Vancouver after he failed to check out as scheduled. He had been staying at the hotel since July 6, according to police.
By the time Monteith's body was discovered by hotel staff he was "clearly deceased," LePard said.
An autopsy is scheduled for Monday. Authorities declined to talk about anything found in Monteith's room but said hotel security records indicate he had returned alone in the early morning hours and was believed to be alone at the time of his death.
Monteith had publicly discussed his struggles with drug and alcohol addiction and in late March had gone back into treatment.
At that time, the actor's girlfriend and "Glee" costar, Lea Michele, released a public statement expressing her "love and support" for Monteith, saying she would "stand by him through this.
After a monthlong stay, he exited the facility and was spotted by the paparazzi vacationing in Mexico with Michele, 26. In June, the two walked the red carpet in Los Angeles at the Chrysalis Butterfly Ball, a high-profile charity event.
Because of his rehab stint, Monteith did not appear on the final episodes of the fourth "Glee" season. His character, Finn Hudson, was last seen on an episode that first aired in April in which he and Glee club leader Will Schuester (Matthew Morrison) agree to team up to lead the singing group to a regional competition.
Monteith had been open about his earlier struggles with addiction. In a 2011 interview with Parade he spoke about his decision to check himself into rehab at age 19 after years of using "anything and everything, as much as possible. I had a serious problem."
Shortly into LePard's remarks Saturday night, the acting police chief paused to offer his condolences to the friends and family of the Canadian-born actor.
"As was the case in countless homes, I watched 'Glee' regularly with my daughters, and I know there will be shock and sadness in many households with the news of his tragic death," he said.
Monteith was active on Twitter as late as Friday, commenting on Syfy's "Sharknado" television movie. "what the crap is Sharknado," he wrote at 1:24 p.m. on July 12. "oh. IT'S A SHARK TORNADO."
Monteith, a native of Calgary, Alberta, rose to fame when he landed the role of Finn on "Glee" in 2009. The actor quickly endeared himself to fans with his portrayal of an aloof, kind-hearted high school quarterback who also had a love for singing.
Late Saturday evening, Monteith's costars began to express shock and disbelief on Twitter. Seemingly in response to the news, Mark Salling, who plays Puck on the program, simply wrote "no" at 10:41 PM.