The 24-year-old came through the Seagulls' youth system and made over 150 appearances for the Sussex club after making his debut in 2005.
He missed the whole of last season after rupturing his Achilles at Notts County in May 2011.
Elphick told the Bournemouth Daily Echo: "This club is hungry for success and all the players have a common purpose - getting into the Championship. I am fortunate enough to have done that and know what it takes. I wouldn't have come here if I didn't think we could do it.
"You need to be consistent because it is a tough league. This club has assembled a good squad and it isn't as if they are going for it with just 11 players. The lads will realise that everyone is going to play a part over the course of the season."