Poly Styrene, the ungainly, vivacious British singer whose band X-ray Spex mocked both society’s conventions and punk rock’s excesses, died April 25 in England. She was 53.

In February, Styrene revealed that she was battling metastasizing breast cancer.

Born Marianne Elliot-Said of English and Somali parents, she grew up in Kent’s Bromley neighborhood, which also spawned the punk-era stars Siouxsie Sioux and Billy Idol.

After cutting a reggae-influenced single, “Silly Billy,” as Mari Elliot in 1976, she was drawn into London’s punk ferment, and rechristened herself Poly Styrene. Her band X-ray Spex, which also featured saxophonist Lora Logic, was among such prominent female-fronted punk acts as the Slits and Siouxsie and the Banshees.

The band made an immediate splash with their 1977 single “Oh Bondage, Up Yours!” The song mocked the then-current punk fashion for bondage gear (stoked by Sex Pistols manager Malcolm McLaren and designer Vivienne Westwood in their Kings Road shop Sex) and displayed a proud punk-feminist spirit.

The nose-thumbing album “Germ Free Adolescents” followed in 1978. With her braces and Day-glo togs, Styrene became a popular, attention-getting figure who defined punk’s freewheeling, socially alert spirit. But what she later described as a breakdown while on tour in 1978 ended the band’s moment in the spotlight. She was later diagnosed with bipolar disorder.

X-ray Spex reformed sporadically in the ’90s and ’00s, and cut the reunion album “Conscious Consumer” in 1995.

Styrene issued the solo albums “Translucence” in 1980 and “Flower Aeroplane” in 2004; material on the latter release reflected her commitment to the Hare Krishna movement. Her final album, “Generation Indigo,” was issued in March; Styrene announced at that point that she would not support its release with a tour, due to her illness.

She is survived by a daughter, singer Celeste Bell-Dos Santos of the Spanish group Debutant Disco.