Liverpool’s first signing of the 2019 summer transfer window was ginger-haired 17-year-old central defender Sepp van den Berg from PEC Zwolle for a fee which could rise to £4.4million depending on various clauses being met. The Dutchman had also been a target for Ajax, Bayern Munich and PSV Eindhoven, Van den Berg made 22 Eredivisie appearances for Zwolle in the 2018/19 season. He made his first-team debut for Liverpool as a late substitute in the 2-0 win at MK Dons in the third round of the Carabao Cup. He played the full ninety minutes of the next two rounds against Arsenal and Aston Villa, as well as against Shrewsbury in an FA Cup replay.

In 2020/21 van den Berg failed to build on the previous season and saw Nat Phillips and Rhys Williams move ahead of him. Despite Liverpool having injury problems in the centre back position, he failed to make any matchday squads prior to the end of January, except for a League Cup tie at Lincoln. On 1st February he was loaned to Preston North End for the rest of the season, where he made sixteen appearances in central defence and as a right back. On 21st June 2021, a season long loan was agreed for him to return to Preston for the whole of the coming season. He was a mainstay of the side, starting 43 of the 46 games in the Championship and also appearing against the Reds in the League Cup. Towards the end of the season, he dropped hints to the Lancashire media that he hoped to return to Liverpool and prove he was worthy of a squad place. 

Van den Berg was loaned to Schalke 04 for 2022/23 but spent a frustrating six months on the sidelines with torn ankle ligaments. When he returned to fitness in April he was straight back in the starting line up but couldn't help prevent relegation from the Bundesliga. For 2022/23 he is back in th Bundesliga, a season long loan having been agreed with Jurgen Klopp's former club Mainz. It was a difficult season for Mainz and they only just escaped relegation. Van den Berg however was outstanding, appearing 33 times and scoring three goals. The only game he was absent for was due to a yellow card suspension. In the summer of 2024, with other central defenders ahead of him at Anfield, he indicated his desire to make a permanent move away from the Reds but Mainz were reportedly unwilling to meet Liverpool's £20 million valuation. This led to a £30 million deal being agreed for him to join Brentford. He instantly became a first choice for the Bees' in central defence, making 31 league appearances with a couple of brief spells on the sidelines due to knee and groin problems.