Early career Nwaneri joined
Arsenal at the age of eight. By the age of 14, he was already playing for their under-18 side. Nwaneri played alongside friend and teammate
Myles Lewis-Skelly at the academy.
Arsenal 2022–23 season Nwaneri started the 2022–23 season playing for Arsenal under-18s, but he quickly advanced to the club's under-21 side. Having made a sole appearance in the
2022–23 Premier League 2, he joined the first team for training in September, and made his first senior matchday squad on 18 September when he was named as a substitute for the
Premier League match against
Brentford. Coming off the bench to replace
Fábio Vieira in second-half stoppage time, he became the youngest player to ever appear in the Premier League at the age of 15 years and 181 days – breaking the record previously held by
Harvey Elliott, and the all-time English top-flight record held since August 1964 by former
Sunderland goalkeeper
Derek Forster, by three days. He also became Arsenal's youngest-ever player in any competition, breaking the previous record of 16 years and 177 days, set by
Cesc Fàbregas in the
2003–04 League Cup. In the post-match press conference, manager
Mikel Arteta explained that they had to name Nwaneri and two other under-21 players on the bench because the first team had several injuries, especially the injury of midfielder and captain
Martin Ødegaard, and a "gut feeling" was behind his decision to send Nwaneri on. In June 2023, with his schoolboy terms ending, Nwaneri agreed to a new deal with Arsenal on scholarship terms with an agreement for a professional contract upon his seventeenth birthday on 21 March 2024.
2023–24 season Nwaneri played as a substitute in the 2023–24 season in the Premier League in Arsenal's 6–0 win away against
West Ham United, coming on in the 77th minute. In the post-match press conference, Arteta mentioned "the players on the bench whispering to bring Ethan on, which is a great thing to hear".
2024–25 season On 25 September 2024, Nwaneri scored his first senior goals when he netted a brace against
Bolton Wanderers in the third round of the
EFL Cup, helping the Gunners to a 5–1 victory. He scored an outside-the-box shot against
Preston North End in the following round. He scored his first goal in the
Premier League on 23 November in Arsenal's 3–0 win home against
Nottingham Forest after getting subbed on in the 82nd-minute. This made him the ninth-youngest goalscorer in the league's history at 17 years, 247 days old. On 4 January 2025, Nwaneri scored in a 1–1 draw against
Brighton & Hove Albion, becoming the third player to score at least five goals in a season before turning 18, following
Michael Owen and
Wayne Rooney. Later that month, on 29 January, he netted his first
UEFA Champions League goal, securing a 2–1 away win over
Girona. Four days later, on 2 February, Nwaneri scored the fifth and final goal in a 5–1 win over
Manchester City, curling in a stoppage-time strike from just outside the penalty box. Nwaneri was named
Man of the Match following his performance against
Leicester City, where he hit the woodwork twice and provided an assist for
Mikel Merino in the 2–0 victory. On 4 March, Nwaneri scored the second of seven Arsenal goals away at
PSV Eindhoven in the Champions League Last-16. On 19 June 2025, it was announced that Nwaneri was one of six nominees for the PFA Young Player of the Year award.
2025–26 season On 8 August 2025, Nwaneri signed a new long-term contract with Arsenal.
Loan to Marseille On 23 January 2026, Nwaneri was loaned to
Marseille until the end of the 2025–26 season. The next day, Nwaneri scored 13 minutes into his Marseille debut in a 3–1 victory over
Lens. ==International career==