The 29-year-old arrives in the German capital from Lille, where he spent two seasons having joined from Premier League side Chelsea in 2012.
Kalou scored 34 goals in all competitions for the French club but now switches to Berlin for his first taste of the Bundesliga.
A Premier League, Champions League, FA Cup and League Cup winner with Chelsea, he expressed his delight at moving to the Olympiastadion.
"After my time in England and France, I am absolutely looking forward to playing for Hertha and in the Bundesliga," Kalou told the club's official website.
"The club has been working actively to sign me, I had very good discussions with the club's managers."
Kalou could come into Jos Luhukay's side for Saturday's visit of Mainz in the Bundesliga, with Hertha having picked up just a point from their opening two matches.
"Kalou is a top striker who has proven his class in the Premier League, the Champions League and with his national team," added sporting director Michael Preetz.