The singer, who scored a chart double last week with his debut LP Doo-Wops & Hooligans and single 'Grenade', celebrated by showcasing the record in London's Café De Paris.
The Sun quotes him as saying: "Thank you London. I know it's sweaty and it's hot but there is no place I'd rather be right now.
"I'm so happy I'm number one in the UK. I love this place."
Mars, who sold 86,000 copies of his record last week, performed album tracks 'The Other Side' and 'Count On Me' and a mash-up of rock classics including Jimi Hendrix's 'Fire'.
The star was recently named the most successful songwriter of last year.