Ujah’s signing comes as reinforcement for the Berlin outfit as they look to benefit from his top-flight experience ahead of their return to the German Bundesliga next season.
Since he made his Bundesliga debut in January 2012, Ujah has scored 51 goals in 171 Bundesliga games, including the four league efforts he notched last season.
"I was able to convince myself about Union on site here in Berlin. The impressions at the Alte Forsterei were very positive and so it was clear to me after my visit: I would like to play here,” Ujah told the club website.
“I'm looking forward to an exciting challenge and want to put my experience and my performances to help the team in order to deliver a successful season.”
Ujah will hope to help the Iron Ones maintain their top-flight status when the 2019-20 Bundesliga season begins on August 16.