The Chemical Brothers are the second act confirmed to play Optimus Alive! 2011.
The duo will play on 8 July, joining the previously-announced Foo Fighters who will headline on 7 July.
Optimus Alive! 2011 will take place on July 7-9 at Passeio Maritimo de Alges in Lisbon, Portugal.
Three-day tickets with camping are onsale now, priced at £103, while day tickets are £45 per day.