Kay Hagen began his career in 2006 as a trainee at GBG Hansegrund GmbH.

After successfully completing, he joined Grossmann & Berger GmbH in 2009 as a real estate consultant. In 2017, he switched internally to the Industry I Warehouse and Logistics Department where he was responsible for selling and letting.

In 2018 he switched to VÖLCKERS & CIE.

On 1 July 2019, VÖLCKERS & CIE became part of Avison Young - since then Kay-Hagen has been working for Avison Young.