Early career

Deacon began his career as a schoolboy at Arsenal in 2008, progressing through the youth ranks and playing regularly for the club's U18 side.^{[3][4][5][6][7]} He signed his first professional contract with the club in July 2010, agreeing an initial one-year deal.^[8] During the 2010–11 season, he made 16 appearances for the reserve side, scoring four times.^[9][10] He was also part of the U19 team that reached the semi-finals of the Dallas Cup, scoring three goals.^[11] Despite playing regularly at reserve level, he did not make any first-team appearances, and was subsequently released by Arsenal on 17 June 2011.^[9] Just two weeks after his release from Arsenal, Deacon joined fellow Premier League side Sunderland on a one-and-a-half-year contract.^[12][13] Deacon made 20 appearances for Sunderland's second string during the 2011–12 season, scoring three goals, but failed to break through into the first-team. He made a further eight appearances for Sunderland's U21 team during the first half of the 2012–13 campaign. In January 2013, having made no first-team appearances, Sunderland announced that he had left the club upon the expiry of his contract.^[14]

Stevenage

In March 2013, Deacon signed for League One side Stevenage on a free transfer.^[15][16] He made his debut for the club, and first professional appearance, in the club's 1–0 home victory over Hartlepool United on 1 April, coming on as an 80th-minute substitute.^[17]

On 12 May 2014, Deacon signed a new contract extension at the club.^[18]

Crawley Town

On 28 July 2015, Deacon joined League Two team Crawley Town on a one-year deal.^[19] He made his competitive debut for Crawley in their opening game of the season on 8 August 2015, providing the assist for Gwion Edwards' goal in a 1–1 draw with Oxford United.^[20][21] He scored his first goals for Crawley on 22 August 2015 in a 3–0 victory over Cambridge United; he opened the scoring in the 39th minute with a deflected shot before scoring Crawley's second after 47 minutes.^[22] Following the match, Deacon stated "It's my first two goals for Crawley and I am over the moon really but the team were great".^[22] He appeared in 40 matches across the 2015–16 season and scored 5 goals,^[23] but was not offered a new contract at the end of the season.^[24]

Sutton United

Following trial spells with Cambridge United and Portsmouth,^[25][26] Deacon signed for National League newcomers Sutton United.^[27] Deacon made his debut for the club on the opening day of the 2016–17 season, a 3–1 home defeat to Solihull Moors.^[28] Deacon scored his first league goal for the U's when he finished off a team counter-attack in the last minute of added time in a 3–1 victory over Lincoln City at Sincil Bank on 13 August 2016, securing Sutton's first win in the fifth tier of English football in 16 years.^[29] One week later he was voted man of the match after his saved shot was finished by Ross Stearn and he assisted a goal for Bedsenté Gomis in a 2–0 home victory against Macclesfield Town, which saw Sutton briefly rise to third in the league, then the club's highest level in its history.^[30] On 8 October, Deacon scored his second goal for the club with a fine solo effort and assisted two more for Ross Stearn and Craig McAllister in another man of the match performance when Sutton routed Surrey rivals Woking 4–1 at Gander Green Lane.^[31] The following day he featured in The Non-League Paper's "team of the day" with a 9/10 rating.

Having scored the winner in a 2–1 home victory against Forest Green Rovers in the FA Cup fourth qualifying round on 15 October,^[32] Deacon netted his first brace for Sutton on 5 November when he struck twice in a first round victory over Dartford at Princes Park; Sutton went on to win 6–3.^[33] On 3 December, Deacon scored a dramatic winner in the final minute of added time in the second round tie, a 2–1 home victory over League Two side Cheltenham Town, to send Sutton through to the third round of the FA Cup for the first time in 22 years.^[34] The following day Deacon featured on The Non-League Paper's front page and again in the team of the day, alongside Simon Downer and manager Paul Doswell.^[35][36] Deacon said later: "It was 100% the best moment of my career, putting Sutton into the Third Round of the FA Cup, it was the stuff dreams are made of for anyone."^[37] Deacon was voted player of the month by Sutton supporters.

In the third round, Sutton were drawn to face League One side and local rivals AFC Wimbledon, ranked 50 places above Sutton in the league pyramid, at home; the tie, played on 7 January 2017, ended 0–0.^[38] The replay took place at Kingsmeadow on 17 January. Sutton were a goal down when midway through the second half, Deacon fired in a stunning strike from the edge of the penalty area to level the score. He assisted a second goal for Maxime Biamou to help the U's complete a historic comeback and win the match 3–1, putting Sutton through to the fourth round of the FA Cup for the first time since 1989.^[39] Deacon was nicknamed "magic man" by Paul Doswell and Sutton supporters.^[40]

In the fourth round on 29 January, Deacon featured prominently in Sutton's 1–0 victory over Championship side Leeds United, who were ranked 84 league places above Sutton, putting the U's into the fifth round of the FA Cup for the first time in the club's 118-year history. Deacon was named in the FA/OPTA Team of the Round.^[41] On 20 February, Sutton played Deacon's boyhood club Arsenal in the fifth round. Deacon hit the crossbar during the second half but could not stop Sutton falling to a 0–2 defeat.^[42] He was voted player of the month for January/February and finished the season as joint top scorer in all competitions alongside Biamou. Deacon won the Players' Player of the Year and Supporters' Player of the Year awards and his goal against AFC Wimbledon was voted goal of the season.^[43]

Dundee

On 14 June 2017, Deacon signed a deal with Scottish Premiership club Dundee.^[44] Deacon scored his first Dundee goal at Pittodrie to equalise against Aberdeen in a 2–1 defeat. Deacon left Dundee on 31 January 2019 by mutual consent.^[45]

Return to Sutton United

In February 2019, he returned to Sutton United.^[45]

Havant & Waterlooville

He joined National League South side Havant & Waterlooville in summer 2019.^[26]

Maidstone United

On 10 June 2021, Deacon joined Maidstone United.^[46] He would help Maidstone win the 2021–22 National League South.^[47] After being relegated the following season, Deacon would leave Maidstone in June 2023.^[48]

Havant & Waterlooville return and Dulwich Hamlet loan

On 13 June 2023, Havant & Waterlooville announced the re-signing of Deacon following his release from Maidstone United.^[49]

On 16 March 2024, Deacon joined Isthmian League Premier Division club Dulwich Hamlet on loan until the end of the season.^[50] He made his first start the same day in a league win over Lewes.