The men's 400 metres hurdles event at the 2023 European Athletics U23 Championships was held in Espoo, Finland, at Leppävaara Stadium on 14 and 15 July.

[1] Prior to the competition, the records were as follows: Qualification rule: First 3 in each heat (Q) and the next 4 fastest (q) advance to the Semi-Finals.

[2][3] Qualification rule: First 3 in each heat (Q) and the next 2 fastest (q) advance to the Final.

[4][5] [6] Wind: +0.5 m/s