The 53-year-old actor and the 38-year-old South African actress, who recently sparked romance rumours after being spotted on several dinner dates in Los Angeles upon returning from a New Year's holiday in Hawaii together, kissed on the lips and were very affectionate with one another after taking their seats at the charity event in the Montage hotel in Beverly Hills.
The couple did not walk the red carpet together but the 'Milk' star sat with his arm around Charlize, who has an adopted two-year-old son Jackson, for the evening and gave her a few kisses on her neck before leaning in to give her a ''sweet kiss'' on the lips, according to E! News.
The gala marked the pair's first official public appearance together.
A source said: ''They are spending night after night together and moving very fast. It seems like it's getting serious and that they can't get enough of each other.''
Sean, who was previously married to Robin Wright and Madonna, was briefly linked to Charlize in 2010 and has also dated Scarlett Johansson.
The 'Prometheus' actress has been single since ending her relationship with Irish actor Stuart Townsend in 2010 after nine years together.
Other guests at the charity gala included Julia Roberts, Chris Hemsworth and his pregnant wife Elsa Pataky, Diane Kruger, Chris Martin and wife Gwyneth Paltrow, Emma Thompson, Michael Douglas, Winona Ryder and U2, who performed at the event, which raised almost $6 million for Sean's J/P Haitian Relief Organisation, which was founded in 2010 to provide medical care, food and water, and develop housing following the earthquake.