Ipswich born Adrian Pennock made only one appearance for Norwich City ( a 4-1 defeat against Southampton on 17th February 1990) before moving onto Bournemouth in 1992 for £25,000. He had signed for the Canaries as Associate Schoolboy in November 1986 although he had been at Ipswich's school of excellence originally. Despite competition from Ipswich, Norwich signed him when Ipswich failed to make him an offer. Adrian progressed through the ranks at Carrow Road. He even had the obligatory "coming of age" loan period to Scandinavia (Molde Fotballklubb).

After 131 appearances for the South Coast club, Adrian suffered a career threatening injury. He managed to recover from this and then signed for Gillingham in October 1996. He has now made over 150 appearances for Gillingham (155 by the end of 2000/01)

Gillingham reached the Division Two play-offs in 1998/99 but lost on penalties to Manchester City At Wembley after a 2-2 draw. Adrian was one of the unlucky players to miss a penalty for Gillingham. At the end of January 2001, Adrian was linked with a move to Reading.

Adrian retired at the beginning of 2003, aged 31 following his 11th operation since damaging cruciate ligaments in his right knee at Bournemouth eight years previously. A chance to remain playing football in Kent materialised within days with both Dover (Dr Martens League) and Gravesend & Northfleet (Conference) expressing an interest in Pennock. Essex side Canvey Island (Rymans League) were also linked (The Non-League Paper). The conference side eventually won the battle for Pennock's services signing him and former Bristol Rovers striker Dwayne Plummer on Tuesday 21st January 2003. Pennock was also appointed to coach Gravesend's Under 19 side.

On 31st October 2003, Adrian received a treat when he was appointed assistant manager to replace Phil Handford who was leaving Gravesend.

In January 2005, Nationwide South club Welling United announced the appointment of Adrian Pennock and Phil Handford as the new managerial team at Park View Road. Pennock joins as first-team manager, whilst Handford, a former Welling favourite as a player who has also coached at Margate, will be Pennock's
assistant-manager.

Adrian left Welling at the end of the 2006/7 season to become an academy coach at Stoke City. He became first team coach in the summer of 2011. He left Stoke following Pulis' sacking in May 2013.

Pennock was appointed manager of Conference side Forest Green Rovers on 12th November 2013. Despite taking them to second place in the Conference in the 2015/16 season and thus into the play-offs for promotion to the Football League, Pennock was sacked on 27th April 2016 with Forest Green chairman Dale Vince stating "It was a difficult decision just a week out from the play-offs after Ady had taken us to our highest placed finish in the National League. However, as a club we felt we needed to make this change, in order to give us the best chance of succeeding in the play-offs. We thank Ady for his efforts while at the club and wish him well in the future."

On 4th January 2017, Gillingham named Pennock as their new Head Coach replacing Justin Edinbuirgh. He will be joined by Welling United boss Jamie Day and Bromley assistant manager Steve Lovell as first-team coaches. The trio have been placed in charge until the end of the 2016/17 season. Chairman Paul Scally said "A change was necessary to ensure the club achieves the best possible position. The current squad is the most expensive in the history of Gillingham FC, it has enormous potential and is capable of achieving great success over the remainder of the season and beyond."

Gillingham finished 20th in 2016/17 and Pennock stayed on as head coach with Peter Taylor coming in as Director of Football. A poor start to the 2017/18 season saw Pennock leaves the Gills by mutual consent on 25th September 2017 with Gillingham in 22nd place in League One

On 27th October 2017, Pennock was appointed as manager of Conference side Barrow replacing Mickey Moore who departed on 17th October after just eight weeks in the role, having lost to seventh-tier side Shaw Lane in the FA Cup fourth qualifying round. Barrow are 22nd in the Conference.

After seven months, Pennock was sacked by Barrow on 18th May 2018 with the club finishing one place and one point above the relegation zone.

At the end of the 2018 Singapore Premier League, it was announced that Pennock would manage Brunei DPMM FC for the 2019 campaign. Brunei had finished third in 2018 but were inconsistant under manager Rene Weber. He left DPMM in 2021 but returned in 2023.

On 1st March 2024 Pennock returned to Kent to become manager of National League South side Dartford.