[7] On 14 July 2023, it was announced that Timber had joined Arsenal from Ajax on a long-term contract and would wear the number 12, previously worn by William Saliba.

[9] On 6 August, he made his competitive debut for the club against Manchester City in the Community Shield, which Arsenal won 4–1 on penalties.

[12] On 22 April 2024, Timber made his comeback in Arsenal Under-21s' Premier League 2 game against Blackburn Rovers, playing the first half and scoring the opening goal in a 2–2 draw at Ewood Park.

[13][14] He made his first-team comeback on 19 May, coming on as a 69th minute substitute for Ben White in Arsenal's final-day win against Everton.

"[15] On 4 December 2024, Timber scored his first goal for Arsenal from a header from a corner against Manchester United in a 2-0 victory at the Emirates Stadium.

[21] Timber was included in the final selection of the Netherlands team for the 2022 FIFA World Cup by manager Louis van Gaal in November 2022.

[25] He again played 90 minutes in the round of 16 win against the United States[26] as well as the entirety of the quarter-final match against Argentina, which the Netherlands eventually lost on penalties and so were subsequently eliminated from the tournament.

[28] In the match against Bosnia & Herzegovina on 8 September, he appeared as a substitute in the 83rd minute, lining up alongside his brother Quinten for the first time in senior football.