The 30-year-old "Applause" singer took to Instagram to celebrate the special family moment, posting a black and white photo with her baby goddaughter.
"So proud to be made one of the Godmother's of our little angel Sistilia. @briannewmanny and his Wife Angie have been my friends since we were kids on the lower east side.
"It was a beautiful baptism and Italian style feast. We love u sissy!" she captioned the picture.
In the photo, Gaga, whose real name is Stefani Germanotta, was wearing a white button-up shirt with baby's breath flowers in her hair.
"The boys are back in town. Love that my daddy hangs out with my crew. Or that I hang out with his...I'm not sure anymore!" she wrote.