On the international scene, Delfouneso first came to notice playing for the England U16 team – collecting eight caps and scoring three goals during this period, two were scored in the 2006 Victory Shield. In October 2007, Delfouneso marked his debut for the England U17 team with a hat-trick in a 6–0 victory over Malta.

Born in Tyseley, Birmingham, Delfouneso – a product of the Aston Villa Academy – became a regular for both the club’s reserve and academy teams in the 2006–07 season. He made his debut for the reserve team in March 2007, just a month after turning 16. His late goal gave Villa a 2–1 win against Portsmouth. In October 2007, he scored his first goal in a 1–1 draw with Reading. In February 2008, Delfouneso signed his first professional contract with Aston Villa, a few days after he was given the number 14 shirt for the first team – it was later reported in French magazine Onze Mondial, that the number was chosen due to Delfouneso’s admiration of striker Thierry Henry. He also travelled with the squad for the game at Fulham, but missed out on the final 16. By the end of the 2007–08 season, Delfouneso had made 41 appearances for the Academy team, scoring 22 goals in the process.

Delfouneso made his competitive first-team début as a substitute in the away tie of the UEFA Cup second round match against Icelandic opponents FH Hafnarfjörður. This made Delfouneso the youngest player to represent Aston Villa in European competition, at the age of 17 years and 195 days. He also came on in the second leg at Villa Park. He made his first competitive start in a UEFA Cup tie against MŠK Žilina, scoring with a left-footed volley after just half an hour of his debut. He scored again in his second start on 17 December 2008, netting a consolation goal away at Hamburg.

Delfouneso made his debut for the England U19 team on 8 October 2008 in a UEFA Championship Qualifying tie against Albania. The striker came on as an 18th-minute substitute and netted the second goal in a comfortable 3–0 victory. He added another brace to his tally in the semi-final match against France to put England through to the final of the 2009 UEFA Under-19 Championship.

Delfouneso made his first domestic senior appearance on 4 January 2009, in an FA Cup tie against Gillingham at Priestfield Stadium, which Villa won 2–1. He scored his first domestic senior goal a month later, on 4 February 2009 in an FA Cup fourth round replay against Doncaster Rovers at Villa Park, which Villa won 3–1. His performance was rewarded with high praise from boss Martin O’Neill.

On 16 February 2009, it was reported that Crystal Palace manager Neil Warnock was interested in taking Delfouneso to Selhurst Park on loan. Villa boss O’Neill refused, declaring that Warnock’s chances of acquiring the striker were “not a prayer”.

Delfouneso made his league debut against Tottenham Hotspur as a second-half substitute for Gabriel Agbonlahor, on 15 March 2009. He was given a second run-out during Villa’s 3–3 draw with Everton, creating two good chances for himself, but failed to score.

On 13 May 2009, Delfouneso marked a debut seasonby picking up both Aston Villa Players’ Young Player of the Year and Aston Villa Supporters’ Young Player of the Year at the annual end-of-season Awards Night. Delfouneso furthered this eight days later as he netted the opening goal in a 3–1 victory over Sunderland in the Premier Reserve League final.

On 6 November 2009, Delfouneso signed a new two-and-a-half-year contract with Aston Villa, keeping him at the club until the end of the 2011–12 season.

On 2 January 2010, Delfouneso was in the starting eleven for Aston Villa’s third-round FA Cup tie against Blackburn Rovers. In the game, he scored his fourth senior goal for the club, which was his team’s first goal in a 3–1 win. Delfouneso scored with his head, diverting an in-swinging Ashley Young cross just inside the opposition keeper’s near right post from ten yards. Shortly after the game, Villa boss Martin O’Neill admitted that Delfouneso along with fellow youngsters Marc Albrighton and Ciaran Clark were the subject of many loan offers from various other clubs. However, he went on to emphasise his confidence that the trio were good enough to remain as vital squad members on the fringes of Aston Villa’s first team.

On 23 January 2010, Delfouneso scored the opening goal in the fifth minute in Villa’s FA Cup fourth-round tie against Brighton & Hove Albion. He was an unused substitute in the final of the League Cup, as Villa lost 2–1 to Manchester United at Wembley Stadium on 28 February. He scored his first league goal on 18 April, after coming off the bench against Portsmouth in a 2–1 victory at Fratton Park.

On 6 November 2010, Delfouneso started his first Premier League game against Fulham due to Emile Heskey, John Carew and Gabriel Agbonlahor being injured. He completed 88 minutes of the match, which ended as a 1–1 draw. On 10 November 2010, Delfouneso scored his second Premier League goal in a 3–2 win against Blackpool at Villa Park. On 21 November 2010, he made a substitute appearance against Blackburn Rovers at Ewood Park, replacing Gabriel Agbonlahor on 78 minutes in a 2–0 defeat. On 27 November, he played in Villa’s 4–2 loss to Arsenal at Villa Park. On 29 January 2011, in the FA Cup fourth round, Delfouneso played and scored with a header against Blackburn Rovers with the third goal in a 3–1 win. At the end of this campaign for Villa, he made 16 appearances and scored two goals in all competitions.

On 22 February 2010 Delfouneso received his first call up to the England under-21 squad, On 3 March 2010 he scored on his debut for them against Greece in a 2–1 defeat.

On 8 March 2011, Delfouneso signed for Burnley of the Football League Championship until the end of the season. He made his debut the same day, playing at Hull City’s KC Stadium. Delfouneso scored past on-loan Aston Villa teammate Brad Guzan just five minutes into his first start for The Clarets.

In July 2011, he signed a new three-year contract with Aston Villa. On 13 August 2011, he was an unused substitute in Villa’s opening 2011–12 Premier League fixture with Fulham at Craven Cottage in a goalless draw.

On 23 August 2011, he scored in the League Cup tie against Hereford, helping Villa to win 2–0.

Delfouneso scored his second U-21 international goal against Iceland at Deepdale in a 1–2 friendly defeat in March 2011.

He scored his third goal for the England under-21 team on 5 September 2011 in a 4–1 win against Israel at Oakwell.

On 23 January 2012, Delfouneso signed a one-month loan deal with Leicester City. He made five appearances for the Foxes, all as a substitute, but did not manage to score a goal.

On 31 August 2012, Delfouneso signed a one-year loan deal with Championship side Blackpool. He made his debut the following day as a 66th-minute substitute in a 1–0 defeat to Leicester City at the King Power Stadium. He scored his first goals for the club on 18 September, scoring twice in a 4–1 win against Middlesbrough.

On 16 August 2013 it was confirmed that Delfouneso had re-signed on loan with Blackpool on a six-month deal. He played eleven league games in his second spell at Bloomfield Road, before returning to his parent club on 2 January 2014.

On 30 January 2014, Delfouneso joined Coventry City on loan for the remainder of the 2013–14 season. Delfouneso struggled for fitness during his spell and managed only two league goals in 14 appearances. His first came against Walsall in March, with his second and last goal for Coventry coming in a 2–1 defeat at Bramall Lane at the end of the 2013–14 season. He was also credited for a goal against Wolverhampton Wanderers that was later awarded as a Danny Batth own-goal.

On 20 May 2014, Aston Villa announced via their Twitter page that Delfouneso, along with Marc Albrighton, had been released from his contract and would be a free agent for the start of the 2014–15 season.

After two previous loan spells at Bloomfield Road, Delfouneso signed a one-year contract with Blackpool with the option of a second in July 2014. He made his first start for the club in his new spell with them on 9 August. He was released in May 2015.

On 6 August 2015, following Delfouneso’s release from Blackpool, he signed for Blackburn Rovers on a one-year deal and was handed the number 7 shirt. On 11 August 2015, he scored his first Rovers goal with a header against Shrewsbury Town in a 2–1 defeat at Ewood Park in the Football League Cup first round. He also found the back of the net at Huddersfield on 15 August 2015, his second goal for the Rovers, in a Championship clash. On 18 March 2016, Delfouneso joined Bury on loan until 19 April.

On 18 August 2016, Delfouneso signed for Swindon Town until the end of the 2016–17 season.

On 21 January 2017, Delfouneso re-joined Blackpool on a permanent deal for the second time and fourth time overall, signing a deal until the end of the 2016–17 campaign. His contract was extended by Blackpool at the end of the 2017–18 season after they exercised an option.

In May 2019 he signed a new two-year contract with Blackpool.

On 6 August 2020, Delfouneso joined Bolton Wanderers on a two year deal. After scoring four goals in Pre-season his competitive debut came on 5 September in Bolton’s first match of the season, a 1–2 home defeat against Bradford in the first round of the EFL Cup. He scored his first competitive goal on 3 October, scoring Bolton’s second goal in a 2–1 win against Harrogate Town.