31-year-old Adam came runner up in American Idol in 2009 (losing out on the top spot to Kris Allen) and he will now be continuing his successful career by appearing in the award-winning musical drama series.
The exciting news was revealed on Twitter by Glee's co-creator, Ryan Murphy, who wrote: "I am thrilled to announce that the super talented Adam Lambert is joining the cast of Glee this fall."
And it sounds like the show's female lead, Lea Michele (who plays Rachel Berry), is just as happy to welcome Adam into the season five cast.
She tweeted: "Omg so excited that @adamlambert is going to be on #Glee this season! I hope he's with me in NYC! #GleeSeason5"
Since coming second on American Idol, Adam has enjoyed a successful music career both in the US and internationally, which even includes touring with Queen and topping the US Billboard Hot 200 chart.
It is still unclear whether the singer has bagged a regular slot on Glee or if he will just be making a special one-off appearance on the show like a number of celebrities before him.
Adam will be following the the footsteps of stars such as Britney Spears, Gwyneth Paltrow, Ricky Martin and even Queen's Brian May, who have each been guests in the previous series.
Glee returns to our TV screens in September. We can't wait!
Are you excited to see Adam in season five of Glee? Let us know below.
Watch Adam's music video for 'Whataya Want From Me?' below: