Terfel has not performed at the event, Wales' leading international festival, in ten years.
The festival runs July 4-9. Also scheduled to appear are Manchester's Hall_ Orchestra, pianist Llyr Williams, and mezzo-soprano Katherine Jenkins, accompanied by London's National Symphony Orchestra.
Other highlights include screening of Charlie Chaplin films accompanied by new scores by composer Carl Davis, the Choir of the World competition, and choral and folk music performances.
Performers at previous Eisteddfods have included Plšcido Domingo, who made his U.K. debut there in 1968; Luciano Pavarotti, who appeared in the choir competition in 1955 (and for whom the first prize is named); and Kiri Te Kanawa.