Bareilles' fellow singer-songwriter Groban was nominated in 2017 for Best Actor in a Musical for his performance in Natasha, Pierre & The Great Comet of 1812.
This year's gala honoring excellence on Broadway is to air live on CBS from Radio City Music Hall.
"The theater has completely transformed my life in every way possible. I have never felt more embraced and encouraged by a professional community, and I am so grateful for that," Bareilles said in a statement Wednesday. "I feel incredibly lucky to get to spend an evening celebrating and applauding this outstanding collective of artists, friends, collaborators and creatives."
"Sara Bareilles and Josh Groban electrified and inspired audiences last year when they brought their incredible talents to Broadway," added Jack Sussman, executive vice president of specials, music and live events for CBS Entertainment. "These two have great chemistry together, and we can't wait to see what they have in store as hosts for this year's Tony Awards."
Broadway stars Katharine McPhee and Leslie Odom Jr. are to announce the names of the 2018 Tony nominees on May 1.