The now 53-year-old Ruhnert switched to Union as chief scout in the summer of 2017. A year later, he took over the position of director of professional men's football and, together with the head coach Urs Fischer, who was appointed in 2018, was responsible for the sporting fortunes of 1. FC Union Berlin's men's team.

Extraordinary successes were achieved during this time; promotion to the Bundesliga, reaching the UEFA Conference League, Europa League and Champions League, as well as top flight survival for seven consecutive years.

After avoiding relegatin in literally the last second, Ruhnert returned to the position of chief scout at his own request in the summer of 2024. In this role he supported his successor, Horst Heldt, as squad planner.

“The sporting path of our men's team since 2018 has given our club a tremendous boost in development. Oliver Ruhnert played an important part in this, and we are very grateful to him for his commitment over the years,” said Union president Dirk Zingler. “Our cooperation was very intensive, passionate, and always characterised by the struggle for the club’s success. We wish him all the best for his future path. He will always be always warmly welcomed at the Alte Försterei.”

“For me, a chapter of my life is ending, which I would not have dared to dream of in the summer of 2017," said Ruhnert, bidding goodbye to Köpenick. "Together, we have achieved successes here that hardly anyone would have thought possible and that no one can take from us. The core of it all for me was a very close and trusting exchange with the club management, but also within the entire club. I will take many unforgettable moments with me from these years and will remain closely connected to Union, the people who shape the club, the employees, and the fans.”

“My path to Union is closely linked with Oliver's, and we have worked together in the last one and a half years as we envisioned. Therefore, I would like to sincerely thank him for his support," said Hrst Heldt, Union's director of men's professional football. "Oliver has helped Union show what is possible for a club when it manages to pool all its resources. We will continue to work on that.”