Early career Knibbs was raised in
Derbyshire and joined the
Nottingham Forest academy at age nine. He was released at age 14 before moving to the
Aston Villa Academy. He was released from Aston Villa in 2019 after spending seven years in their youth system.
Cambridge United In June 2019 Knibbs signed a two-year contract with
Cambridge United. He sustained a heel injury shortly after signing, forcing him to miss most of pre-season. On 13 August, he made his debut for Cambridge in an
EFL Cup match against
Championship side
Brentford. He scored the winning penalty as Cambridge beat Brentford 5–4 in the shootout. He made his
league debut on 17 August in a 2–1 win over
Colchester United. He suffered a hamstring injury on 22 February 2020, in a 0–0 draw to
Plymouth Argyle, which caused him to miss the rest of the season. He finished his debut season with Cambridge as the top scorer, scoring nine goals in 31 games. He extended his contract in October by two years, keeping him at the club until 2023. He scored his first league goal of the season on 16 January 2021 in a 1–1 draw to Colchester. Knibbs struggled that season, due to the sacking of
Colin Calderwood and the arrivals of
Paul Mullin and
Joe Ironside. He finished the season with 31 appearances and 3 goals in all competitions. He once again struggled for gametime, but manager
Mark Bonner praised him for his conduct. His first league goal of the season came on 18 January 2022 in a 3–1 win over
Doncaster Rovers. He won Cambridge Player of the Month for September for three goal contributions. Cambridge rejected an offer for Knibbs from Plymouth in January 2023. He left the club following the expiry of his contract in June. In total, he made 156 appearances and scored 26 times for Cambridge. He made his Reading debut in a 1–0 defeat to
Peterborough United on 5 August. His first goal came on 26 August in a 2–1 defeat to
Exeter City. On 10 October, he scored the first professional hat-trick of his career in an
EFL Trophy match against
M4 rivals Swindon Town that finished in a 5–0 win. He finished his debut
Reading season with 53 appearances and 16 goals in all competitions, establishing himself in the first-team.
2024–25 season Knibbs started the season opener on 10 August 2024, a 1–1 draw against
Birmingham City. Later that month, manager
Rubén Sellés revealed that Knibbs suffered a groin injury in training, and would be out for three to four weeks. He made his return on 14 September in a 1–0 defeat to
Leyton Orient, coming on as a substitute for
Charlie Savage. He scored his first goal of the season on 28 September, scoring the equaliser in a 2–1 win over
Huddersfield Town. Despite playing through a "painful"
MCL injury, he scored three goals in three games in November and was subsequently nominated for
EFL player of the month. Reading continued to push for a position in the play-offs, and Knibbs was an important member of the team, scoring three goals in five games (in wins over
Wrexham,
Peterborough &
Wycombe). In the process, he also became the first Reading player since
Dave Kitson to score 15 goals or more in all competitions in back-to-back seasons since 2005/06.
Charlton Athletic in 2025 at
The Valley. On 1 August 2025, Knibbs signed a four-year deal at
Charlton Athletic.{{cite news |title=Harvey Knibbs is an Addick! ==Personal life==