The group - on which the nominated film "Bohemian Rhapsody" is based - then brought the crowd to its feet with a rendition of the classic "We Are The Champions".
The run-up to the 91st awards had been a series of missteps and backtracks by the Academy of Motion Picture Arts and Sciences.
"I lived in Los Angeles for 17 years and to open the Oscars, I never would have dreamed this is possible", Lambert, 37, told E! "The fact that I'm celebrating him and this story with you tonight is proof that we're longing for stories like this".
Filmmakers used a combination of Mercury's real voice, Malek's voice and another singer against the band's original recordings to showcase Queen's hits.
Time’s Up president resigns after her son is accused of sexual misconduct
Lisa Borders, then-CEO and president of Time's Up, was announced last Friday as the speaker for the 2019 Commencement address. But he told the Times , "My client vehemently denies that any inappropriate or nonconsensual touching occurred at any time ".
Malek has already won the best actor awards at both the BAFTAs and the Golden Globes for his role in "Bohemian Rhapsody".
Queen biopic Bohemian Rhapsody is up for five awards at this afternoon's ceremony.
The last time the Oscars went without a host, in 1989, the opening of the show was widely regarded as an interminable disaster, punctuated by an unsettling duet between Rob Lowe and Snow White. The Academy has also been criticised for being predictable when it comes to choosing the winners, mostly going by the media trend and not surprising the fans.