(written from a Production point of view)
According to "It's Federation Day!", a newspaper article created as background material for Star Trek Generations, Thomas Vanderbilt was the ambassador for United Earth at the Federation Charter signing ceremony, and was appointed the first President of the United Federation of Planets on October 11, 2161. The clipping quoted Vanderbilt as saying, "We are truly entering a brave new world of peace, exploration, and security with the establishment of this Federation."
Although the article containing this information was present within the Picard family album during filming on Generations, neither the character of Thomas Vanderbilt nor the rest of the article is considered canon, because the article was never seen on-screen.