The Paramore singer and Gilbert announced their split in a joint statement posted on Williams' Instagram account.
"We want to publicly state - plainly, and only this time - that we are splitting up. We also feel it important to state that we are going to be okay and in fact, we remain close friends who are good in each other's eyes.
"We will continue to encourage and support each other personally and professionally," they wrote.
Williams and Gilbert tied the knot in February last year in Tennessee. They began dating in 2008 and got engaged in December 2014.