Barnes was born in Barking, London.
His professional career began on his 17th birthday when he signed a professional contract with Derby County after being a trainee.
He made his first-team debut under Phil Brown aged 17 as an 84th-minute substitute for Paul Peschisolido in a 1–0 defeat at home to Grimsby Town in the 2005–06 League Cup, with his league debut coming in a 1–1 draw away to Crewe two weeks later as a 73rd minute replacement for Marcus Tudgay.
Barnes intermittently made first-team appearances as Derby struggled but began to command a regular place when Phil Brown was replaced by Derby's academy manager Terry Westley in January 2006.
Westley was familiar with Barnes from his time as a youngster at Derby and made him an integral part of the team as Derby managed to avoid relegation to League One.
Barnes played a role in 16 matches under Westley, with his first start coming in Westley's first match in charge (a narrow 1–0 home defeat to Sheffield United) and his first professional goal coming in a 2–2 draw away to Watford.

His performances during the end of the 2005–06 season drew interest from the Premier League during the close season, but with the appointment of Billy Davies as manager and new investment, Barnes signed a four-year extension to his current contract.
Barnes became a regular in the Derby team that won promotion to the Premier League, playing in 46 matches (with 34 of those starts) putting him behind only the club's player of the year Steve Howard in terms of appearances.
He also scored eight goals, including four in two weeks with a 92nd-minute equaliser in a 2–2 draw away to Cardiff City, a brace in a 2–1 home win over Barnsley, and the winner in a 2–1 home win against West Bromwich Albion.
During this time he gained a reputation for supposedly saying "Whoosh" as he ran past defenders.
In a 2017 interview, he indicated this was a one-time response to aggression from an opponent, and has been taken out of context.
His performances in March 2007 earned him the Championship Player of the Month award for that month.
Although he picked up an injury towards the end of the season, Barnes was still able to make an impact in Derby's successful Championship play-off campaign in his two substitute appearances.
It was his corner from which Leon Best scored an own goal in the second leg of the semi-final clash with Southampton and he also came off the bench to set up Stephen Pearson's winner in the 1–0 2007 Championship play-off Final victory over West Brom.
After this, it was found out that Barnes was playing with a broken foot and he missed all of the summer injured as Derby prepared for life back in the top flight.
He was named Derby's Young Player of the Year for the 2006–07 season.

These injuries carried over into the start of Derby's disastrous 2007–08 season.
He made his first Premier League appearance on 22 September 2007 as a substitute against Arsenal in the 75th minute and scored his first goal in a 2–2 draw against Newcastle United.
The injuries that plagued Barnes through the course of his season, as well as no pre season and being put in the team two months earlier than was recommended, affected his form and he failed to play as vital a role in Derby's season as he had during 2006–07 and his season ended early when it was discovered he had a knee injury which required major surgery, meaning that he would miss the remainder of the 2007–08 season and the start of 2008–09.

Barnes returned to the Derby team in January 2009 and scored twice at Old Trafford in the League Cup semi-final second leg as Derby fell to a 4–2 defeat on the night, 4–3 on aggregate.
After just three league appearances, on 31 January 2009, Barnes signed for Fulham on loan for the rest of the 2008–09 season with a view to a possible permanent transfer in the summer, with Derby receiving a substantial loan fee, and agreeing a fee of £2 million, raising to £4 million on appearances if he signed permanently.
He did not make a single appearance for the Cottagers due to fitness, but scored seven in eight reserve matches.
On 24 May,
Barnes was born in Barking, London. His professional career began on his 17th birthday when he signed a professional contract with Derby County after being a trainee. He made his first-team debut under Phil Brown aged 17 as an 84th-minute substitute for Paul Peschisolido in a 1–0 defeat at home to Grimsby Town in the 2005–06 League Cup, with his league debut coming in a 1–1 draw away to Crewe two weeks later as a 73rd minute replacement for Marcus Tudgay. Barnes intermittently made first-team appearances as Derby struggled but began to command a regular place when Phil Brown was replaced by Derby's academy manager Terry Westley in January 2006. Westley was familiar with Barnes from his time as a youngster at Derby and made him an integral part of the team as Derby managed to avoid relegation to League One. Barnes played a role in 16 matches under Westley, with his first start coming in Westley's first match in charge (a narrow 1–0 home defeat to Sheffield United) and his first professional goal coming in a 2–2 draw away to Watford.
His performances during the end of the 2005–06 season drew interest from the Premier League during the close season, but with the appointment of Billy Davies as manager and new investment, Barnes signed a four-year extension to his current contract. Barnes became a regular in the Derby team that won promotion to the Premier League, playing in 46 matches (with 34 of those starts) putting him behind only the club's player of the year Steve Howard in terms of appearances. He also scored eight goals, including four in two weeks with a 92nd-minute equaliser in a 2–2 draw away to Cardiff City, a brace in a 2–1 home win over Barnsley, and the winner in a 2–1 home win against West Bromwich Albion. During this time he gained a reputation for supposedly saying "Whoosh" as he ran past defenders. In a 2017 interview, he indicated this was a one-time response to aggression from an opponent, and has been taken out of context. His performances in March 2007 earned him the Championship Player of the Month award for that month. Although he picked up an injury towards the end of the season, Barnes was still able to make an impact in Derby's successful Championship play-off campaign in his two substitute appearances. It was his corner from which Leon Best scored an own goal in the second leg of the semi-final clash with Southampton and he also came off the bench to set up Stephen Pearson's winner in the 1–0 2007 Championship play-off Final victory over West Brom. After this, it was found out that Barnes was playing with a broken foot and he missed all of the summer injured as Derby prepared for life back in the top flight. He was named Derby's Young Player of the Year for the 2006–07 season.
These injuries carried over into the start of Derby's disastrous 2007–08 season. He made his first Premier League appearance on 22 September 2007 as a substitute against Arsenal in the 75th minute and scored his first goal in a 2–2 draw against Newcastle United. The injuries that plagued Barnes through the course of his season, as well as no pre season and being put in the team two months earlier than was recommended, affected his form and he failed to play as vital a role in Derby's season as he had during 2006–07 and his season ended early when it was discovered he had a knee injury which required major surgery, meaning that he would miss the remainder of the 2007–08 season and the start of 2008–09.
Barnes returned to the Derby team in January 2009 and scored twice at Old Trafford in the League Cup semi-final second leg as Derby fell to a 4–2 defeat on the night, 4–3 on aggregate. After just three league appearances, on 31 January 2009, Barnes signed for Fulham on loan for the rest of the 2008–09 season with a view to a possible permanent transfer in the summer, with Derby receiving a substantial loan fee, and agreeing a fee of £2 million, raising to £4 million on appearances if he signed permanently. He did not make a single appearance for the Cottagers due to fitness, but scored seven in eight reserve matches. On 24 May,
Giles Barnes