Kevin Greening was born in Kent, and grew up in Bristol where he worked voluntarily for the Bristol Hospital Broadcasting Service and later studied chemical engineering at St Catharine's College, Cambridge, where he was station manager at Cambridge University Radio. His first job was as a construction worker on the Humber Bridge. He then trained as a studio manager and began his broadcasting career at the BBC World Service. After a brief spell as a Programme assistant at BBC Radio Solent, in 1989 Greening joined London's Local station BBC GLR as a producer, before becoming a presenter of their Breakfast show in 1991.

In April 1993, Greening joined the newly launched Virgin Radio, presenting a Friday and Saturday evening show and a Sunday morning show. After two months, he took over their weekday afternoon show, where he remained until he quit Virgin in December 1993.

In January 1994, Greening joined BBC Radio 1, presenting the Weekend Breakfast Show (Saturday & Sunday 7-10am). In the summer of '94, Radio 1 agreed to cover the Gay Pride event for the first time and these reports into the general days output were fronted by Greening; the success of these led to Radio 1 becoming a regular fixture at Gay Pride events. In May 1995 Greening was named in Gay Times' Top 200 Gay Men and Lesbians as an out gay DJ.

In November 1994, Greening took over the Weekend Lunchtime show (Saturday & Sunday 12-2pm). Again he featured many of his comedy characters (usually voiced by Andrew McGibbon) featured on Weekend Breakfast. October 1995 saw Greening move back to Weekend Breakfast where he would remain for another 16 months. Greening was given the Drivetime show in February 1997. Regular features on the show included the "Joke du Jour", "60 Second Cinema", and the "Evening Procession".

Early mornings seemed to play a big role during Greening's time at Radio 1, as he had presented Weekend Breakfast and had also been the main stand-in presenter for Steve Wright, Chris Evans and Mark Radcliffe on Weekday Breakfast, but October 1997 saw Greening present the Weekday breakfast show alongside Zoe Ball, where he would remain for 12 months.

Greening moved to a Sunday morning show from 6.30-10am in September 1998. At the time he was also presenting shows for BBC World Service and a TV show for digital station BBC Choice. On Sunday 16 January 2000, Greening presented his final Radio 1 show. In the last half hour he played some of the sketches from his time with the station. Not long after he left Radio 1, in 2000 Greening moved to BBC Radio 5 Live, where he was a stand-in presenter for various daytime slots.

In March 2001, whilst undertaking supply work at Five Live, he began co-presenting a Saturday Morning show on GLR's replacement, BBC London Live, alongside Amanda Hussain, the show went out from 8-11am on Saturday mornings and lasted until September the same year when the show was taken over by Danny Baker. Throughout late 2001 into 2002, Jazz FM employed Greening for various stints, then in May 2002, he briefly joined London's Heart 106.2 presenting their 2-6pm Weekend afternoon show. Greening was awarded a Fellowship by the Radio Academy in 2001; he was the only non-executive ever to be so honoured in the academy's 25 years.

After a stand-in stint on the BBC 6 Music Night Train Programme and in addition to XFM, in April 2004, Greening re-joined Jazz FM where this time he presented a Sunday morning show from 10am-2pm. Not long after, he also took over from Clive Warren on the Saturday Morning show, which also went out from 10am-2pm.

On 7 June 2005, Greening took over the 10am-3pm slot on Jazz FM's replacement, 102.2 Smooth FM. From 26 March 2007, he moved to a 1pm-4pm weekday afternoon slot on the relaunched 102.2 Smooth Radio where he built up a cult following. His "game with no name" quiz show was particularly funny, where listeners had to suggest the most suitable song to play against a particular news item. He also presented Saturday afternoons from 2-5pm on the station.

Greening was openly gay and had a previous long-term relationship with Andy Lowe, whom he often referred to on air as his "lesbian life-partner" or "live-in chum". When their relationship came to an end in 2005, after a brief separation they continued to share their house in North London.

At the time of his death Greening had been in a relationship with Sean Griffin for some time.

Chris North, Greening's agent, announced that Greening had "died peacefully in his sleep", aged 44, one day before his 45th birthday. His boyfriend, Sean Griffin, was arrested the following day in connection with his death, and for possession of a Class A drug, but charges in relation to Greening's death were not pursued by police.

It was later revealed following the post-mortem that Greening died of a heart attack after taking large quantities of cocaine, ecstasy and GHB. He had spent part of the night prior to his death at the Recon event held at The Arches nightclub in Southwark, London.