Flood's first mainstream commercial break came in 1987 when he engineered U2's "The Joshua Tree", alongside producers Brian Eno and Daniel Lanois. In that same year, he gave up mixing U2's album to produce Erasure's The Circus - wich was the duo second album and the first one to have great commercial success. Shortly thereafter, he co-produced Nine Inch Nails on debut "Pretty Hate Machine", along with John Fryer, Adrian Sherwood, and Keith LeBlanc. He also worked with Depeche Mode on their 1990 album, "Violator". In 1991, he returned to work again with U2 on "Achtung Baby", along with Brian Eno, Daniel Lanois and Steve Lillywhite. The following year, he also returned to work with Depeche Mode to record the album "Songs of Faith and Devotion" and co-produced three tracks of Nine Inch Nails' "Broken" EP.