The fan favourite was given the opportunity to join the web series - which follows a group of aspiring artists in LA - after he was eliminated from the Fox competition during the Top 16 round.
Around 20,000 fans had signed a petition urging that the 19-year-old singer be given a second chance at success.
Speaking on Hulu before his entry, he said: "I really feel like a lot of this wouldn't have happened without all the fans, and when one person can take time to make a petition, write all of it out, and all that stuff, it really feels good."
A peak of over 1.5 million viewers watched the Texan's arrival at the house, where he was greeted at the door by his fellow housemates and given a tour of the property. He later played 'Across The Universe' with Kara.
The show - created by Simon Fuller - will follow Lambert as he navigates the music scene in LA. Other artists to be featured include Justin Gaston, who shot to fame dating Miley Cyrus.
New episodes of If I Can Dream - which streams 24/7 - are uploaded to Hulu every Tuesday morning, while American Idol continues this Tuesday on Fox.