The 58-year-old was seen kissing his long term love Lauren Silverman outside the bash, as they were joined by their close friends.
Lauren looked incredible wearing a slinky gold sequined dress, while her hair was styled in Hollywood style curls.
BGT judge Amanda Holden, who had flown in especially, also looked amazing wear a sexy pink slip dress.
Earlier in the day Simon, once known as the Mr Nasty of talent show American Idol, was joined by a whole host of famous faces as he got the accolade.
Leona Lewis, One Direction's Louis Tomlinson and America's Got Talent judges Heidi Klum, Howie Mandel and Mel B were all there at the unveiling – before joining him for dinner.
His son Eric was also there for his big moment as was Lauren’s son Adam, from her previous relationship.
Clearly delighted with the turn out, Simon said: "Thank you, all of you, for turning up and making this happen. It means an awful lot to me.
The music mogul basked in the limelight as he recalled his time as a reality show judge, record producer and creator of long-running franchises The X Factor, America's Got Talent and Britain's Got Talent – admitting it was all rather surreal.
Accepting the honour, Simon said: "I was a massive fan of American television, American movies, when I was growing up. I remember the first time I came to Hollywood, a long time ago and thinking it was the most magical place. And now I'm looking down at this, it's so surreal.
"Lauren, you have been my rock over the last few years. And one thing I was thinking about today was who would have got the biggest kick out of this and it's my mum and dad, and they are not here.
"I have a feeling they are looking down. And now I look over to my son, Eric, and say, 'maybe one day you will get one of these as well'."
Simon, whose star is number 2,642 on the Walk Of Fame, became a household name as a judge on American Idol from 2001-2010 thanks to his harsh critiques of aspiring singers, often prefaced with the line "I don't mean to be rude but…".
He went on to launch The X Factor in Britain and the United States, and the British and U.S versions of Got Talent, as well as signing boy band One Direction and girl band Fifth Harmony to his Syco record label and the hugely successful Little Mix.
He added: "It's been a blast, the last 18 years. And if anyone says fame is a bad thing, I don't know what they are talking about because it's the best thing in the world."
Speaking at the bash, Kelly – who introduced him on stage – said Simon had a talent for spotting authentic people with raw talent and developing them.
The 36-year-old joked she was one of the few artists Cowell had never been rude to, before praising him for "appreciating authenticity".
"He appreciates you being yourself, and that's very rare. In this industry I think people just want you to fit in to something," the Grammy-winning singer said.
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