On January 11th 2005, England Under-21 striker Dean Ashton became Norwich's record transfer signing when he completed a £3million move from Crewe to Carrow Road. This could rise to £3.5million with Crewe receiving 20% of any profit made on selling Ashton. After two days of negotiation, Dean signed a three-and-a-half year contract, with a further one-year option, after completing a medical. The deal for the highly-rated 21-year-old shattered Norwich's previous record transfer fee of £1m paid to Leeds for defender Jon Newsome in 1994.

The 20-goal striker was delighted to get the chance to try his luck in the Premiership, having been linked with a number of top-flight clubs including Aston Villa, Blackburn Crystal Palace, Everton, Liverpool and Tottenham. "With Norwich I felt there was a chance to play regularly," Ashton said. "The main thing I've noticed is how professional the club is. All the facilities are excellent."

Ashton had scored 74 goals for Crewe in all competitions since signing from a trainee in the summer of 2000. He has also come up through the international ranks with England, featuring for both the U19s and U20s before establishing himself in the U21 squad. He has three U21 caps and two goals.

Dean made his Norwich debut in the 3-0 defeat at Aston Villa on 15th January but got his first goal in the 4-4 draw with Middlesbrough on 22nd January.

Following Norwich's relegation at the end of the 2004/5 season, Dean was linked with a £4m switch to Scottish champions Rangers. The next club to be linked were West Ham over the weekend of 16h/17th July 2005. After Dean scored twice in Norwich's opening three games of the 2005/6 season, The People suggested that Wigan would fork out £5million for his signature to replace Hawthorns-bound Nathan Ellington. With Norwich bidding for Birmingham's Clinton Morrison, it was suggested that Ashton would be leaving Carrow Road with Tottenham, West Ham (£6m) and Man City (£7m) linked with him over the weekend of 20th/21st August 2005. His absence from Norwich's Carling Cup clash with MK Dons only led to more speculation but on 25th August, Dean signed a one year extension to his contract.

In November 2005, Dean and colleague Robert Green were linked with a January 2005 transfer to Everton after David Moyes was spotted in the crowds during Norwich's 2-0 defeat to Wolves. The following month saw Aston Villa, Man City and West Ham all linked with a swoop in the January transfer window. Nigel Worthington stated that Ashton was worth three times what Norwich had paid for him. Charlton manager Alan Curbishley declared that Ashton was too expensive for the Valiants on December 17th 2005 but the following day's News of the World suggested a £6million switch to Wigan. His value and demand would have shot up following his hat-trick for Norwich against Southampton on 17th December 2005. On 31st December 2005, the Daily Telegraph in their article on the January transfer window linked Ashton with moves to Wigan, West Ham and Man City. Portsmouth, with additional funds available from their new Russian owner, were said to have offered £5million for him. Further speculation that Ashton would be sold came when he did not appear in Norwich's line-up for their FA Cup clash with West Ham on 7th January. However Nigel Worthington said that his absence was due to a groin strain injured in training. West Ham were then said to have bid £5m for him but were told that Norwich wanted £7.5m. Their bid was said to have increased to £7m by 20th January.

On the evening of 21st January 2006, Norwich finally agreed terms with West Ham that made Ashton City's record sale as he departed to Upton Park for a fee of £7million which could rise by £250,000 based on whether Dean is capped by England (£125,000) or whether West Ham make it into Europe with him in their squad (£125,000). There is also a 15% sell off clause of any profit that West Ham might make from any future sale. Crewe received £1.5million as part of the deal that took Ashton to Carrow Road.

Ashton paid tribute to the support he has received from City fans. “I have had a great year with Norwich and I would like to sincerely thank the fans and everyone I have worked with at Colney and Carrow Road,” he said. “West Ham are a big club, I am ambitious and at the end of the day the chance of a swift step up to the Premiership is too good to turn down. I spoke to Nigel and the Board and told them I wanted to pursue this opportunity. I'd like to thank Norwich for understanding that and allowing myself and my representative to talk to West Ham.”

Dean scored his first goal for the Hammers on 4th February 2006 in a win over Sunderland at Upton Park. Ashton's contribution to West Ham's FA Cup run that toook them to a final against Liverpool meant that the Hammers would be in Europe in the UEFA Cup in the 2006/7 season and so Norwich received an additional £125,000. Although he suffered a hamstring injury in the semi-final, he recovered fitness to start in the FA Cup final aginst Liverpool on 13th May 2006., Ashton assisted in the build-up with West Ham's first - an own goal by Jamie Garragher, and then scored West Ham's second to put them two nil up but an inspired performance by Steven Gerrard saw Liverpool equalise. Although West Ham went ahead again through Paul Konchelsky, Gerrard equalised at the end of the match. The game went to penalties and Liverpool won 3-1 after misses by Zamora (who had replaced Ashton in the second half), Konchelsky and Ferdinand

On 11th June 2006, the Daily Star suggested that Newcastle United would bid £10m for Ashton whom they see as a replacement for Alan Shearer.

Reports in The Mail on Sunday, The People and The News of the World on Sunday the August 2006 all suggested that Ashton would be called up to Steve McLaren's first England squad for the August friendly against Greece. This would earn Norwich another £125,000. The speculation proved correct and Ashton was ready to make his debut but suffered an injury during the England training sessions that resulted in him missing the rest of the 2006/7 season. This didn't stop speculation on 18th February 2007 by the News of the World that Newcastle manager Glenn Roeder would make a triple raid on West Ham if the East Londoners were relegated, to sign Ashton, Anton Ferdinand and Nigel Reo-Coker.

Ashton returned to the West Ham first team during the 2007 pre-season and after a period where he scored three goals in four games, was recalled to the England squad. However he suffered a sprained medial knee injury in the latter stages of West Ham's 1-0 defeat at Aston Villa on 6th October 2007 which will see him ruled our of action for six weeks. West Ham's head physiotherapist George Cooper said: "We received the results of Dean's scan and they were what we expected which is that he had sprained the upper third of his medial ligament. In the majority of cases it will take up to six weeks for full recovery."

Dean returned to form in the second half of the 2007/8 season and was called up to the England squad for the friendlies with the USA and Trinidad & Tobago. Rumours in May 2008 suggested he was a £10m target for Manchester United - a move which would net the Canaries £400,000 in sell-on clauses. Previous stories have linked the former Crewe striker with Newcastle, Manchester City and Portsmouth.

Dean made his international debut in the aforementioned friendly clash with Trinidad, playing the first 45minutes of the game played on Sunday 1st June. Three days later, Dean signed a new five year deal with the Hammers. However this did not end the speculation. Man City were rumoured to be preparing a £15m bid and then it was reported that following the sale of Robbie Keane to Liverpool, Tottenham lodged a £15m bid for Ashton on 6th August 2008 but that this was rejected outright by the Hammers. Hammers chief executive Scott Duxberry, who said: “Hell would have to freeze over for us to sell Dean to a major rival.”

There was widespread speculation on 24th August 2009 that Ashton would have to retire prematurely from football due to his injuries. After months of speculation, West Ham United officially announced on 11 December that striker Ashton was to retire from the professional game. He had failed to recover from an ankle injury originally sustained by a tackle by Shaun Wright-Phillips whilst on an England training session in August 2006. Several operations and comebacks later, Ashton was forced to quit the game having last played in September 2008.

At the end of February 2012, Dean was voted into Norwich City's Hall of Fame

Ashton tried his hand at coaching but instead works primarily as a pundit.