Following the announcement, the "Heart Attack" singer can be seen blowing out candles on the cake next to a "Eurovision" slate.
The comedy also stars Ferrell, Rachel McAdams and Pierce Brosnan. It marks Lovato's first live-action movie appearance since 2010's "Camp Rock 2 The Final Jam".
"Eurovision" tells the tale of a pair of aspiring Icelandic musicians, Lars Erickssong and Sigrit Ericksdottir, who are given the opportunity of a lifetime to represent their country at the annual Eurovision song contest - the world's biggest song competition.
Brosnan will essay Ferrell's father, the most handsome man in Iceland.
David Dobkin, who directed "Wedding Crashers", is helming the film. The shooting is currently underway in the UK and Iceland.