The 'Yeah!' hitmaker is "so excited" to be taking the reins of the ceremony, which will take place at Los Angeles' Shrine Auditorium on 29 March, and will also be among the performers on the night.
He said in a statement: "I'm so excited to host the 2020 iHeartRadio Music Awards and help celebrate the music that I and millions of other music lovers listened to this past year. It'll be like hanging out with old friends."
As well as Usher, other performers at the awards show will include Justin Bieber, Halsey and Lizzo.
Meanwhile, Billie Eilish leads the nominations at this year's awards with eight.
The 18-year-old singer will contest for the prestigious Song of the Year accolade for her track 'bad guy' alongside Lil Nas X's 'Old Town Road' Shawn Mendes and Camila Cabello's 'Señorita', Jonas Brothers' 'Sucker' and 'Truth Hurts' by Lizzo.
Billie will also compete against Lizzo - who has six nominations - in the Female Artist of the Year award, for which Taylor Swift, Halsey and Ariana Grande are also in the running.
Male Artist of the Year will be fought out between Ed Sheeran, Khalid, Luke Combs, Post Malone and Sean Mendes.
Lil Nas X is snubbed in that category but tied with Lizzo for the most nominations behind Billie overall.
Best Duo/Group of the Year will be contested between Dan + Shay, Imagine Dragons, Jonas Brothers, Maroon 5 and Panic! At The Disco.
The awards will air on Fox live from the Shrine Auditorium in Los Angeles on March 29, and will also broadcast through the US on iHeartMedia radio stations and the iHeartRadio on demand and streaming service.
