Since it was announced that Warner Television and DC Comics were working with Greg Berlanti (Green Lantern, Arrow, The Flash) and CBS to develop a new DC Comics television series starring Supergirl, the Kryptonian cousin of Superman, it was widely specualted as to whether or not Supergirl would exist in the same universe as Arrow and The Flash, since the shows would be airing on different networks. Well, there is no longer any speculation. It has been confirmed that Executive Producer Greg Berlanti does indeed plan to have Supergirl set in the same universe as his CW shows, which most refer to the DC Television Universe but which I have taken to calling the Berlantiverse.
While Marc Guggenheim, Arrow Co-Creator and showrunner as well as Co-Writer of the Green Lantern movie with Greg Berlanti, has said that it is possible that Supergirl could crossover with Arrow and Flash, it has now been reported by Comic Book Movie that Greg Berlanti actually had this stipulation in his contract when negotiating the series with CBS. It is now clear that Berlanti has intended for Supergirl to exist in the Berlantiverse since the beginning. This isn't that far fetched of an idea, all three shows are being developed by Warner Bros (who also produces The Big Bang Theory and Two and a Half Men and a few other shows for the CBS network) and the CW network is co-owned by Warner Bros and CBS (that's what the C stands for). So with CBS and The CW being sister networks, there really is no conflict at all with getting this done.
This is sure to be welcome news to fans of the CW shows and will likely bring in a whole new audience for the Supergirl series, and it honestly might give Supergirl a much bigger chance at being greenlit, since female-led superhero movies and television series don't have a track record of doing all that well. NBC tried this once before with the failed Wonder Woman pilot from David E. Kelley and who can forget the abortion that was the CW series Birds of Prey? With The Flash and Arrow being big television draws for The CW, it really is in the show's best interest to be included in the Berlantiverse. So with Firestorm, The Atom, Flash and Arrow already existing in this universe, and Supergirl on the way, it shouldn't be too long before we see Oliver and Barry put together their own Justice League, which will only mean good things for fans and audiences alike. Stay tuned to Movie Pilot and we will have more news as it develops.