Lars Windhorst's firm Tennor Holding purchased the stake in Hertha, which could increase to 49.9 per cent in the future.
"We see it as a long-term and promising commitment," Windhorst said in a statement.
"For me personally it is also a great pleasure to contribute to the economic future of this great club in Berlin."
Hertha are hopeful the investment will help the club compete more consistently for silverware, with their last major trophy coming when they beat Bayer Leverkusen in the 2002 DFB-Ligapokal final.
"Today is a good day for Hertha," club president Werner Gegenbauer said.
"This partnership is a result of the development that we are making. The president of Hertha is always anxious to ensure the club has a solid financial basis to work off in the future.
"This aspiration and also the preservation of our club culture are reflected in this new partnership."
Hertha has been relegated twice in the past 10 seasons but responded by winning the 2. Bundesliga title at the first time of asking on each occasion.
It finished 11th in the Bundesliga last term, 35 points behind champion Bayern Munich.