He made his first record entitled "And the Tears Came Tumbling Down" for the Fontana label in 1965. He then toured with a band called 'David Essex and the Mood Indigo' for two years and released a further 7 singles in the 1960s. He also recorded two songs, 'A Rose' and 'Leon and John and Billy and Me' which remain unreleased, but exist as acetates. His first notable acting role aside from small appearances in the films Assault and All Coppers Are... was the lead in the stage musical, Godspell in 1971 at the age of 23. Two years later, he starred in the film That'll Be the Day (1973) and recorded his international hit single, the self-penned "Rock On", in the same year. It sold over one million copies, and was awarded a gold disc by the R.I.A.A. in March 1974. It was nominated for a Grammy and reached No. 5 on the Billboard Hot 100. A second single, "Lamplight", also reached the Top 10 in the UK Singles Chart.

In December 1973, Essex appeared in the stage version of Tommy at London's Rainbow Theatre.

Essex's pop idol looks gave him a strong female fan base and his British tours created scenes of hysteria reminiscent of Beatlemania. According to The Guinness Book of British Hit Singles, he was voted the number one British male vocalist in 1974, and was a teen idol for more than a decade.

In 1978, he appeared on Jeff Wayne's concept album, a musical version of The War of the Worlds, as the Artilleryman. In the UK the two-record set remains a bestseller.

In the same year, Essex played the character Che in the original production of the Andrew Lloyd Webber musical Evita, and his recording of the show's "Oh What a Circus" reached Number 3. Two years later, he starred in the motorcycle racing film Silver Dream Racer; and the Soundtrack song "Silver Dream Machine" was yet another Top 3 hit in the UK Singles Chart. Essex, a keen motorcyclist, waived his fee for the then-new 1980 electric start Triumph Bonneville he had contracted to advertise on behalf of the struggling Triumph motorcycle workers' co-operative.

In 1981, he starred in Childe Byron, a play staged at the Young Vic theatre.

In 1985, he co-wrote and starred as Fletcher Christian in the West End musical Mutiny!, based on the novel Mutiny on the Bounty by Charles Nordhoff and James Norman Hall. The score produced two more hit singles, including "Tahiti," his tenth Top 10 success.

Essex continued to perform in all areas of show Business. A 1988 sitcom, "The River", achieved good ratings. In 1991, a compilation entitled His Greatest Hits reached Number 13; a 1993 album, Cover Shot, featuring a cover version of the Buzz Cason/Mac Gayden song "Everlasting Love", peaked at Number 3. His autobiography, A Charmed Life, was published in 2002, and became a bestseller.

Essex spent six years as an ambassador for Voluntary Service Overseas, which earned him an OBE in 1999.

In 2005, he appeared as a guest vocalist and wrote songs for Saint Etienne's album Tales from Turnpike House. Also that year, he appeared in the Channel 4 documentary Bring Back...The Christmas Number One.

Essex was due to join the cast of soap opera EastEnders, in early 2006, as new character Jack Edwards. However, the role was expanded beyond the three weeks planned, and Essex was unable to commit the time. The role instead went to Nicky Henson.

Essex used to record and release records on his own 'Lamplight' record label. He has since changed the name of his company to Joseph Webster Ltd, named after his first grandchild. He tours regularly and continues to act, appearing in Boogie Nights 2, Footloose and Andrew Lloyd Webber's musical Aspects of Love. From September 2008 to the summer of 2009 he took his own musical, All the Fun of the Fair, on a tour of the United Kingdom. He followed this in the autumn with a sell-out tour of the UK, named the Secret Tour. Essex has released a DVD on his website of the last night of the tour, filmed in Bournemouth. He returned to London's West End with his own hit musical All the Fun of the Fair but with a different ending to that performed in the Provinces.

On 20 September 2010, Essex married Welsh Actress Susan Hallam-Wright, his third wife, 26 years his junior, born 1973, at St Cross Church, Talybont, near Bangor, North Wales. He first met her at the end of 2008 whilst she was auditioning for a role in Essex's musical, All the Fun of the Fair. She got the part of Sally, then got promoted to the role of Mary, Jack's girlfriend for the West End version at the Garrick Theatre in London in April 2010. He had previously been married to Maureen Neal (in 1971) and Carlotta Christy (in 1997).

In January 2011, it was announced that Essex had finally joined the cast of EastEnders as Eddie Moon, five years after he was initially supposed to appear in the show. His first on-screen appearance was on 3 June 2011. Eddie left the square on 6 October 2011. He then wrote the music score for the film Traveller (2013), in which he co-starred with his son Billy Cook who played the main role as a half-gypsy trying to find his identity.

Essex was born in Plaistow, east London. His father, Albert, was an East End docker and his mother, Olive (née Kemp), was a self-taught Pianist and an Irish Traveller, descended from Romany Gypsies. His grandfather, Thomas Kemp, was nicknamed "Philimore", which was the anglicised version of "Philly Mor" – being Irish for "Big Philly". Essex was two years old when his parents moved out of the overcrowded home the family was sharing with relatives, to Canning Town where he grew up.

In February 2016, Essex performed in The War Of The Worlds at the Dominion Theatre.