However, the band plans to go ahead with its programme of concerts with Olzon being replaced by Dutch singer Floor Jensen. She has earlier been with the bands Forever and ReVamp.
In the press statement, both the band and Olzon say they are pleased with their time together and for gigs played during that time.
Nightwish is currently on tour in the US, where Olzon recently missed a concert after being hospitalised. Jensen took over lead vocals beginning with Monday evening's show in Seattle.
Olzon joined the band in 2007 taking over from Tarja Turunen after she was fired from the band.