The singer, who appeared on American Idol's tenth season, was announced as the latest signing for the record label on Tuesday.
In a statement confirming the news, she said: "I am thrilled to be joining the Interscope and 19 Recordings family. [Interscope Geffen A&M Chairman] Jimmy Iovine was an amazing mentor during my time on Idol and I'm looking forward to working with him and everyone at Interscope Records and 19 Recordings."
She added: "This is a dream come true."
Toscano's first single will be an acoustic guitar track called 'The Time', written and co-produced by Esther Dean, who has previously provided hits for artists including Rihanna.
A release date for Toscano's debut album has yet to be announced, with the singer recently telling People that she didn't want to "rush" the process: "We want to make sure that we find the perfect sound, the perfect songs. So I'm not sure when exactly, but hopefully soon."
Toscano's exit from American Idol in April shocked many viewers - and judges Jennifer Lopez, Randy Jackson and Steven Tyler - who had considered her to be a frontrunner.
Jennifer Hudson, Tom Hanks and Ashton Kutcher were among the celebrities who voiced their surprise at her early elimination.
Toscano can be seen alongside the rest of American Idol's Top 11 on this summer's American Idol Live! tour, which kicks off tonight in Utah.
Watch Pia Toscano's performance of 'All By Myself' on American Idol: