She attended Brays Grove School in Harlow, Essex; she returned to the school for a final reunion in June 2008 as guest of honour.
De Sykes had a hit in 1974 with the Simon May penned "Born With a Smile on My Face" which reached Number 2 in the UK Singles Chart. She also recorded the theme tune to the television programme The Golden Shot with the group 'Rain' that same year. The theme song, "Golden Day" was written for them by Lynsey De Paul and Barry Blue. Around this time, the television company, ATV Midlands started each day's broadcasting with a short film accompanied by another song performed by Rain with de Sykes singing vocals, "Odyssey" (often incorrectly referred to as "Life is a Beautiful Book"). De Sykes returned to the UK Top 20 a year later as a solo artist with the song "We'll Find Our Day" from Crossroads, which was featured at Meg Mortimer's wedding in the UK TV soap opera in 1975. De Sykes appeared in the show as singer 'Holly Brown'. She also had a starring role in the comedy Side by Side.