Although the couple were photographed on a recent trip to Cabo San Lucas in Mexico, the wedding represents the first time that they have gone public with their romance.
According to an insider, the couple's arrival at the ceremony was met with "stares" from the packed bar.
The actress allegedly muttered "this is so terrifying" to the suit-clad Penn, who held her hand.
An insider close to Scarlett Johansson said ::
"she is "head over heels" for the Oscar winning Penn. The 'Lost In Translation' star had previously distanced herself from rumours of a relationship, noting that she was only interested in the actor's relief effort in earthquake ravaged Haiti."
Watch Scarlett Johansson video:: (sweetest one)