The 26-year-old won the the Polish championship in 2012 with Slask Wroclaw, and will join the German club on a free transfer.
Gikiewicz has penned a two-year deal at the Eintracht-Stadion, meaning he will stay at the club until June 2016.
Speaking to the club's official website, he said: "I am very happy that I came to Braunschweig. All have welcomed me very warmly."
Sports director Marc Arnold added: "We noticed Rafal (when) observing matches. We are firmly convinced that he will help us in the next two years."
Braunschweig are currently involved in a battle to avoid relegation from the Bundesliga.
They currently prop up the table with 25 points from 30 matches.
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