If you want to get technical about it, Looking Glass was NOT a one-hit wonder.
“Brandy” was, to be sure, their biggest hit and the song that most people identify with the band. But “Jimmy Loves Mary-Anne,” the opening track from their second album, spent only one week less on the Billboard Hot 100 chart than “Brandy” did. Okay, it peaked at #33 while “Brandy” spent most of its chart life at or near the top, but still.
“Brandy (You’re a Fine Girl)” was actually a departure from their usual sound, which was a little more Jersey Shore Rock and Roll. This wound up creating a little trouble for audiences who came to see them expecting to hear an entire evening of “Brandy”-grade music, and it probably contributed to the demise of the band.
Founding member Elliot Lurie left the band in 1974 for a solo career, and by the end of the next year the band changed names twice and moved into a power pop/metal sound. That band, called Starz, did have a couple of hits and they do still play from time to time. Lurie, meanwhile, moved into the production and music supervision side of things for awhile, and occasionally returns to live performances.