Mursi was in a run-off over the weekend with Ahmed Shafik, Hosni Mubarak’s last prime minister.
The announcement came via a posting on the party’s Twitter account. The Muslim Brotherhood’s website declared Mursi the “first popularly elected Egyptian president.”
A member of the committee overseeing Egypt’s presidential election confirmed on Monday that the Muslim Brotherhood’s candidate was in the lead but said the count had yet to be finalized.
Unofficial results of the June 16-17 presidential election are expected early on June 18, but election officials say the official result of the poll will be announced only on June 21.