He started his career at St Albans and went on to play for Southend United, Tottenham Hotspur and Crystal Palace. With the Eagles in administration Mr Austin was responsible for palaces recovery, despite not being paid wages he convinced the squad to carry on unpaid; therefore try save what was left of the season. Going from 9th to 20th he still managed to keep palace out of the drop. He retired after the 2002–03 season while at Woking and has since worked as a coach, currently as assistant to Jimmy-Floyd Hasselbaink at Northampton Town.
At the age of 12, Austin managed to get on the Watford books and also played for Sunday League side Forest United. At the age of 17, he came back to Watford and played for the under-18s. He then joined non-league side St Albans City.
Austin was signed by Southend manager David Webb from St Albans for £14,000 in 1990 and made his debut on 10 April, as the "Shrimpers" held Burnley to a 0–0 draw. He went on to play the last 7 games of the 1989/90 season as Southend were automatically promoted to the Third division after defeating Peterborough 2–0 on the final day of the season. He scored his first goal for the club on 4 September 1990 in the Rumblelows Cup against Aldershot. In the 1990/91 season he received an injury and was forced to miss out on the beginning of the season, but after recovering he became an integral part of the team as Southend just missed out on the Division 3 title. He scored two more goals for Southend in the 1991/92 season, both in the league. Southend had briefly topped the Second Division after the early Boxing Day games but eventually fell away to mid table in their first season at this level, ending hopes of a unique third successive promotion and a place in the new FA Premier League.
His form attracted interest from bigger clubs and midway through the season Derby County approached Austin, but he felt he could hold out for bigger clubs. He ended up being signed by Tottenham Hotspur, the club he supported as a child by manager Terry Venables for £375,000. In all competitions, he had made 109 appearances for Southend, scoring three goals.
Austin made his debut on 22 August 1992. His first season at Spurs was rather successful, Tottenham finished in 8th place. The following Season he suffered a broken leg against Oldham, on a day when Tottenham went top of the League. By the time Dean returned to fitness Spurs were in a relegation battle under Ossie Ardilles. However, next season he was back in the team and enjoying his best form ever under Gerry Francis Tottenham reached the semi-final of the FA Cup, only to lose to eventual winners Everton 4–1. Towards the end of this season Austin suffered a knee injury which resulted in three operations. Austin struggled for fitness over the next 2 years before suffering another injury to his other knee resulting in him being out for 6 months and not returning until Feb 98. He saw out his contract and was reunited with Terry Venables at Crystal Palace under the Bosman ruling. In all competitions, he made 154 appearances for Tottenham but without scoring.
Austin linked up with former manager Terry Venables at Crystal Palace, although Venables only stayed for six months. The first six months were particularly difficult but after 18 months Austin became a firm fans favourite when he alone decided to stay at the club when Palace entered administration. He accepted a massive pay cut, and he marked his return to the team by scoring the winner against Norwich City. The club, however went into administration in 1999 and defied the odds, staying in Division 1 despite being tipped to go down. Dean was named club captain in the summer of 1999. But having made 142 appearances for Palace and scoring six times, while not playing under Trevor Francis and suffering with both knee and foot injuries he decided to call time on his professional career.
After Austin had left Crystal Palace he was asked by manager Glenn Cockerill to come and help them out of trouble. He was appointed club captain by manager Glenn Cockerill as the club narrowly avoided relegation from the Conference National on his 33rd birthday and Dean decided then and there to call time on his playing career and retired from playing.
Austin briefly managed at Conference South level, he set about obtaining his higher coaching qualifications. By the age of 39 Austin obtained his Pro License and continues to educate himself with additional coaching and management qualifications. Austin has also been learning the Spanish language since his first employment with Watford as their assistant manager.
After a brief spell coaching in Watford's academy in 2003–4, Austin was employed as director of football of Farnborough Town in June 2004, where within a few weeks and only two weeks before the season started, he was asked to take over as manager. Caught in the middle of an ownership battle which resulted in the chairman Tony Theo leaving the club, Austin dealt with numerous financial issues before leaving in February 2005 with the club just outside the relegation zone. Farnborough lost the next 14 games and were relegated before entering administration.
In the summer of 2005, Austin returned to Southend with Steve Tilson as head of recruitment and coach. He was an integral part of Southend winning two successive promotions from League 2 into the Championship and was responsible for developing young players such as Michael Kightly, Stuart O'Keefe and Gary Hooper.
After three successful years he left Southend to become assistant manager to Brendan Rodgers at Watford F.C.. A successful end to the season saw Reading approach Rodgers and his team to take over from Steve Coppell at Reading. This wasn't as successful as anyone would have liked and after the whole team were relieved of their duties Austin returned to Crystal Palace in 2010 as first team coach and U21 manager. He left in the Summer of 2011 having not been able to agree a role with the then manager Dougie Freedman. Austin decided to take a break from football at this time.
From January 2012 until February 2013, Austin was a regional scout for Bolton Wanderers but left his position to join Chris Kiwomya at Notts County as assistant manager. Austin decided to leave Notts County's backroom team in May 2013 due to personal reasons.
Austin returned to Watford as an assistant coach in January 2015. and was the English voice for Slaviša Jokanović's backroom team and was proud to win promotion from the Championship to the Premiership in the 2014–15 Season. Austin's input and help was repaid by a new contract under the new management team at Watford for the Premiership campaign in 2015–16.
In September 2017, Austin was appointed assistant coach of Northampton Town working alongside the newly appointed Jimmy-Floyd Hasselbaink.