Knott joined the Academy at West Ham United at the age of ten before moving with his family to Spain after his mother was diagnosed with lupus.[4] In Spain, West Ham arranged for a trial with Real Madrid, but after the family returned to London, he elected to join the ChelseaAcademy rather than rejoin West Ham.[4] He was signed by Premier League club Sunderland after Chelsea released him in the 2010–11 season.[5] He had been dismissed from the Chelsea Academy and forced to sign a confidentiality agreement after a "smoke grenade incident".[6]
Knott joined Terry Brown's League Two side AFC Wimbledon on loan on 11 January 2012,[7] and made his debut in a 2–1 win against Port Vale three days later.[8] He scored his first goal in professional football at Kingsmeadow in a 2–1 win over Macclesfield Town on 24 January.[9] The 19-year-old received the "Dons" Young Player of the Year award, despite only playing half the 2011–12 season, having scored three goals in twenty appearances.[10]
On 8 October 2012, Knott joined Conference Premier side Woking on a one-month loan.[11] He made his debut at Kingfield Stadium in a 2–1 win over Cambridge United the following day.[12] His first goals came for Garry Hill's "Cardinals" came against Luton Town on 1 January 2013, when he scored twice in a 3–1 win.[13] He scored another two goals on 2 February, in a 2–1 win over Hyde.[14] He was awarded the club's Goal of the Season award for his curled effort against Hyde, which was also nominated for the Conference's Goal of the Season competition.[15] Knott scored eight goals in twenty league games, and returned to the Stadium of Light, at the end of Woking's season, after a 2–1 defeat to Tamworth.[16]ManagerPaolo Di Canio handed him his Sunderland debut on 19 May 2013, the last day of the 2012–13 Premier League season, coming on as a substitute in a 1–0 defeat to Tottenham Hotspur at White Hart Lane.[17]
Knott joined League Two side Wycombe Wanderers on a one-month youth loan deal on 20 August 2013.[18] He made his Wycombe debut four days later in a 2–2 draw with local-rivals Oxford United, and manager Gareth Ainsworth stated that: "Billy Knott had an immense debut. He has energy, passion, drive, everything that I like in a player, and on top of that he's got Premiership quality with his left foot."[19] He settled into the first-team at Adams Park, and his loan spell was twice extended.[20][21] On 14 September, he scored his first goal for the "Chairboys", in a 3–0 win over Plymouth Argyle.[22] Sunderland re-called him on 13 January, 16 days before his loan spell was due to end.[23]
On 22 January 2014, Knott joined League One club Port Vale on loan for the remainder of the 2013–14 season.[24] He scored his first goal at Vale Park with a left-footed strike from 25 yards (23 m) on 22 March, in a 3–2 win over Tranmere Rovers.[25] In doing so he boosted his chances of winning a contract from "Valiants" manager Micky Adams when his contract at Sunderland expired in the summer.[26] On 1 April, he scored with a 20-yard strike in a 2–1 home win over Crawley Town that was later voted as the club's goal of the season.[27]
Bradford City
Knott signed a two-year contract with League One club Bradford City in May 2014 and stated that "[having heard] manager Phil Parkinson's plans to take the club forward, you can't really turn that down."[28] Knott made his debut on 9 August in a 3–2 win against Coventry City at Valley Parade.[29] Knott scored his first goal for the "Bantams" on 19 August in a 3–1 win away to Crawley Town.[30] On 27 August, he scored in a 2–1 win against West Yorkshire rivalsLeeds United in the Second Round of the League Cup.[31] On 24 January, he played the first 80 minutes of City's 4–2 FA Cupgiant-killing of Premier League champions Chelsea at Stamford Bridge, which he described as the greatest achievement of his career.[32] After the game, he received a signed shirt from "Blues" captainJohn Terry, which he passed on to his Chelsea-supporting father.[33] In the next round he helped Bradford beat another Premier League team, as they ran out 2–0 winners over his former club Sunderland.[34] However, he lost his first-team place to Josh Cullen, and was released at the end of the 2015–16 season.[35]
Gillingham
In June 2016, Knott signed a two-year contract with League One club Gillingham.[36] Manager Justin Edinburgh said he was "a very bright talent".[37] He struggled for form at Priestfield early in the season as he said he was "playing on the left in a diamond... but I would rather play top or bottom of the diamond to get on the ball"; he was then sidelined with a hamstring injury before manager Edinburgh was sacked in favour of Adrian Pennock in January.[38]
Lincoln City
On 2 February 2017, Knott joined National League side Lincoln City on loan for the remainder of the 2016–17 campaign.[39] On 1 April, he scored the only goal of the game against Bromley at Sincil Bank to send the "Imps" to the top of the table; speaking after the game, manager Danny Cowley said Knott was a "super-talented kid... [who] can be whatever he wants to be".[40] Lincoln achieved promotion back to the English Football League as National League champions with a 2–1 home win over Macclesfield Town on 22 April.[41] He secured his release from Gillingham and signed a one-year deal at Lincoln City in June 2017.[42]
Speaking in September 2017, he stated that his growing maturity was the key to his recent good form.[43] However, he struggled for form after being sent off later in the month. He lost his place in the starting eleven.[44] On 11 January 2018, Knott moved to Rochdale on loan until the end of the 2017–18 season.[45] However, he started just once and made three substitute appearances for Keith Hill's "Dale". Having struggled with depression for years, his tough time at Spotland led him to drink heavily and as a result he contacted the Professional Footballers' Association; speaking in May 2018 he stated that "I know I still have a way to go but I will get through this".[46] Lincoln released him at the end of the 2017–18 season.[47]
Concord Rangers
On 4 June 2018, following his release from Lincoln, Knott dropped down two tiers to join National League South side Concord Rangers.[48] On the opening day of the 2018–19 campaign, he made his Concord debut during their 2–0 home victory over Gloucester City, featuring for 86 minutes before being replaced by D'sean Theobalds.[49] Just over a month later, he scored his first goal for the club against former side, Woking, netting a late equaliser in the 92nd minute during the 1–1 draw.[50]
Chelmsford City
On 15 March 2019, Knott signed for fellow Essex-based National League South club Chelmsford City.[51] He made six league appearances to help the "Clarets" to qualify for the play-offs with a fourth-place finish at the end of the 2018–19 season. However, they lost 3–2 to Welling United in the semi-finals.[52] He made 21 appearances during the 2019–20 season, which was ended early due to the COVID-19 pandemic in England.[53] On 3 May 2020, Chelmsford announced Knott's departure from the club; manager Robbie Simpson stated that "Billy is an extremely talented player but he struggled for consistency in terms of fitness last season and therefore I feel we are unable to offer him terms a player of his calibre would expect".[54]
Later career
On 4 September 2020, Knott signed for Isthmian League Premier Division club Bowers & Pitsea.[55] In November 2020, Knott joined National League South side Billericay Town while the COVID-19 pandemic halted the Isthmian League season.[56] He played seven times for "Ricay" before the 2020–21 National League South season was also curtailed.[53]
On 11 August 2021, Knott signed for Isthmian League North Division side Canvey Island.[57] On 31 December 2021, Knott signed for Isthmian League North Division rivals Great Wakering Rovers, after having featured just twice in the league for the "Gulls".[58] After three appearances for Great Wakering,[59] Knott re-signed for Bowers & Pitsea ahead of the 2022–23 season.[60] In October 2022, Knott signed for Essex Senior League club Southend Manor on a dual-registration deal.[61]
In January 2023, he joined Isthmian League Premier Division side Margate, after a one-game spell at Southern Counties East League Premier Division club Erith Town.[62][63] He played three games in all competitions for Margate.[64] Ahead of the 2023–24 season, Knott re-signed for Concord Rangers and went on to feature on 21 occasions as the club were relegated from the Isthmian League
Premier Division.[65][66]
Knott is a left-footed midfielder with a 'high-intensity, high-energy' playing style.[69] He prefers to play as an attacking midfielder, but can also play on the left side of midfield.[70]