2019–2020: Debut season and FA Cup win

Martinelli was reportedly subject to interest from a number of clubs but signed a long-term contract with Premier League club Arsenal on 2 July 2019, for a reported fee of £6 million (R$46.9 million).^[11] Holding an Italian passport, Martinelli was not subject to the scrutinised criteria required for English clubs to sign South American players.^[12] He travelled with the Arsenal first team to their pre-season tour in the United States.^[13] He scored a goal on his non-competitive debut, in a 3–0 pre-season win against Colorado Rapids on 16 July.^[14] Upon signing, Martinelli was originally set to play primarily with the under-21s in his first season, then slowly be integrated from the academy setup to the first-team. However, Martinelli's impressive pre-season and quality in training encouraged Arsenal that he would be ready for immediate first-team integration.^[15]

Martinelli made his Premier League debut on 11 August 2019 in a 1–0 win against Newcastle United, coming on in the 84th minute as a substitute for Henrikh Mkhitaryan.^[16] On 24 September, Martinelli scored a brace in his first competitive start for the club in a 5–0 victory over Championship side Nottingham Forest in the EFL Cup. His performance received praise from head coach Unai Emery, who said: "He's hungry to have that opportunity to help us, he is very humble, he fights. I told him to have some patience for his opportunity to do like he was doing. He did that. He deserved it".^[17]

Martinelli made his second start for Arsenal in a 4–0 home win over Standard Liège in the UEFA Europa League on 4 October, in which he scored another brace.^[18] Martinelli kept up his goal scoring form, netting the equaliser in a 3–2 home win over Vitória Guimarães on 24 October, with another header.^[19] In the League Cup fourth round on 30 October, Martinelli registered another brace in a 5–5 draw with Liverpool, and also scored his penalty in the penalty shootout, which Arsenal eventually lost.^[20] As a result, he became the first player to score four times in his first four starts since Ian Wright.^[21][22] Martinelli's performance received praise from Liverpool manager Jürgen Klopp, who labelled him "[the] talent of the century".^[23]

Martinelli's performances led to him being awarded the Arsenal 'Player of the Month' award for October, receiving 75% of the total votes cast, beating out Mattéo Guendouzi and Nicolas Pépé.^[24] After the appointment of interim head coach Freddie Ljungberg, Martinelli started his first Premier League game, scoring Arsenal's equaliser in an eventual 1–3 win over West Ham United on 9 December. On 21 January 2020, Martinelli scored in a 2–2 away draw at Chelsea, making him the first teenager to reach double figures in a season for Arsenal since Nicolas Anelka.^[25] Picking the ball up outside the Arsenal box following a headed clearance from a corner, Martinelli ran the length of the pitch outpacing Chelsea defenders to slot past Kepa Arrizabalaga. The goal was later voted as Arsenal's Goal of the Season by the club's fans.^[26] On 3 July, Martinelli signed a new four-year contract, with a team option for an extra year, until 2025.^[27] Shortly after, Martinelli was ruled out until the end of 2020, undergoing surgery to repair a lesion in the cartilage of his knee following an injury in training on 21 June.^[28]

2020–2022: Return to fitness, position change and individual success

Martinelli made his return on 19 December, coming off the bench to play 19 minutes in a 2–1 away defeat to Everton.^[29] During the warmup against Newcastle United in the FA Cup on 9 January 2021, he sustained a minor ankle injury and was replaced in the line-up by Reiss Nelson.^[30] Martinelli returned to playing in European competition on 18 February, making a 13 minute cameo appearance off the bench in a 1–1 draw against Benfica.^[31] He scored his first goal of the season in a 3–0 away victory against Sheffield United on 11 April.^[32] While previously playing in central positions akin to a classic number 9, under Mikel Arteta's tutelage, Martinelli was moulded to play more on the left-wing where he had more purchase to cut onto his strong right foot & utilise his rapid dribbling to unnerve defenders.^[33][34]

Martinelli missed pre-season after being selected on international duty in Brazil's winning Olympic Gold campaign. Martinelli scored his first goal (a volley with his second touch of the game) of the 2021–22 season against Newcastle United on 27 November.^[35] This goal of his was eventually ranked 3rd in the official Goal of the Season poll held by the club at the end of the season.^[36] On 18 December, he scored twice against Leeds United three days later, marking his first Premier League brace,^[37] with his first goal marking Arsenal's 7,000th scored in top-division English football.^[38][39] On 10 February 2022, Martinelli was sent off for two yellow cards in the space of four seconds against Wolves.^[40] It was his first red card in his career. The red card gained some controversy as he was given two yellow cards in one passage of play, starting with pushing Daniel Podence after a throw in and then a foul against Nélson Semedo.^[41]

Before the conclusion of the 2021–22 season, Martinelli was handed the number 11 shirt pending the departure of Lucas Torreira to Galatasaray in the summer transfer window. ^[42] His former number 35 was later taken up by Oleksandr Zinchenko upon the latter's arrival.

2022–present: Joint-top scorer, title challengers

On 5 August 2022, Martinelli scored for Arsenal in their 2–0 away win at Crystal Palace, becoming the first Brazilian to net a season-opening goal of a Premier League campaign.^[43][44][45] On 31 August, Martinelli scored a 77th minute winner in a home match against Aston Villa, which gave Arsenal five wins from their opening five matches of the season. ^[46] On 1 October, Martinelli provided an assist for Granit Xhaka in Arsenal's 3–1 victory over North London rivals Tottenham Hotspur. ^[47] One week later on 9 October, he opened the scoring within 58 seconds in Arsenal's home match against Liverpool, which the Gunners would go on to win 3–2, and was awarded Man of the Match for his display. ^[48] On Boxing Day, Martinelli scored in Arsenal's first Premier League match since the conclusion of the 2022 FIFA World Cup, a 3–1 win over West Ham. ^[49] On 3 February 2023, Martinelli signed a new long-term contract with the club, tying him down until 2027.^[50][51] On 25 February, Martinelli scored the only goal of the game in an away win over Leicester City. ^[52] In Arsenal's next match against Everton on 1 March, Martinelli netted a brace as Arsenal ran out 4–0 winners and moved five points clear at the top of the Premier League table. ^[53] By the end of the season, Martinelli had scored 15 goals and provided 6 assists in all competitions, becoming the club's joint-top scorer for the season alongside Martin Ødegaard, and finished third in Arsenal's Player of the Season vote.^[54] Martinelli also became the highest scoring Brazilian player in a single Premier League season, equalling Roberto Firmino's record for Liverpool in the 2017–18 season.^[55]

On 12 August 2023, in Arsenal's first match of the 2023–24 Premier League season, Martinelli assisted Eddie Nketiah by pirouetting past Serge Aurier & Danilo Oliveira in a 2–1 home win against Nottingham Forest.^[56] On 3 September, Martinelli provided the assist for Martin Ødegaard's equaliser against Manchester United, just 35 seconds after going 1–0 down. Arsenal would later seal a 3–1 victory.^[57] On 8 October, Martinelli came on as a substitute and scored the only goal of the game in a 1–0 victory over Manchester City with the help of a deflection off defender Nathan Aké, as Arsenal sealed their first league win against their opponents since 2015.^[58] On 24 October, he made his Champions League debut, in which he scored the first goal in a 2–1 away win against Sevilla.^[59]