Iijima's original demo tape was picked up by JVC Victor in 1982 and she was signed to the record company as a singer-songwriter. Soon afterward, she was asked to audition for the role of Lynn Minmay in The Super Dimension Fortress Macross by the label and the producers chose her to play the role. The series quickly became a mega hit and brought Iijima to stardom. Her debut album, Rosé, containing no Macross tracks, had lyrics and music written by her. It debuted at number 10 on the charts in September 1983, and she started her career as a singer-songwriter.
Iijima moved to Los Angeles in 1989 to expand her music career. After releasing her first independent (and first English language) album, No Limit, she was nominated for the 2000 Los Angeles Music Awards' Best Pop Artist for the album and she was in the final four for the award.
Mari Iijima Live in Tokyo at the Hakuju Hall on July 31, 2010
She won the best Asian song for her track Unspoken Love from the album Wonderful People at the Just Plain Folks Awards in 2006 and performed as a guest performer.
She entered the 50th Grammy Awards with Swim, a track from her 2006 album Uncompromising Innocence. Her listed entries are for the "Best Female Pop Vocal Performance" category (entry number 55) and the "Best Instrumental Arrangement Accompanying Vocalist(s)" category (entry number 175).
In 2006, she reprised her role as Lynn Minmay in ADV Films' English-language release of Macross. which made her the first actor to play the original role in both Japanese and English languages for an entire anime series.
Iijima released her twenty-first studio album, called Echo, in August 2009. The title was taken from the nymph character Echo that appears in Echo and Narcissus. The album's theme is unrequited love.