The 30-year-old is reunited with Uwe Koschinat, who was previously his coach at Fortuna Köln.
Fürth had wanted to retain his services despite his contract ended last month, however they had offered him decreased terms, with Sandhausen pouncing for him instead.
The Frenchman joined Fürth from then-3. Liga Fortuna in 2018 and scored five goals in his first five games, but never quite matched that form again. He ended the 2018-19 with ten goals, and last season with nine goals.
His importance at Fürth had also decreased with the success of Håvard Nielsen and Branimir Hrgota over the past 12 months.
Koschinat believes Keita-Ruel is “a tried and tested second division player” who has a good scoring and is “an absolute ‘beast'” up front. He also knows from working with him before that they have gained “a great dressing room player.”
Keita-Ruel says he is “happy” to join the club, where he sees “a lot of potential.” He says he wants to be “part of this and contribute to successful development with (my) goals.”
With Kevin Behrens and Aziz Bouhaddouz, as well as last season’s breakout player Julius Biada, Sandhausen’s attack will be one to watch next season.
The club haven’t announced the length of his contract.