Steffen was sacked after Bremen's 1-1 draw with Borussia Monchengladbach extended the club's winless run to 10 matches. The slump has left the Green-Whites hovering just above the relegation play-off place after securing only four wins from 20 league games this season.
Thioune takes charge immediately, ending a spell out of work since leaving Fortuna Dusseldorf in October 2025. The role marks his first in the Bundesliga, having previously coached VfL Osnabruck, Hamburger SV and Dusseldorf in Germany's second tier.
Bremen managing director Clemens Fritz said Thioune's football philosophy and leadership qualities made him the ideal candidate to guide the club out of danger.
"We had very good discussions with Daniel. His idea of football, his personality and his approach to our current sporting situation were decisive factors in the decision," Fritz said. "We are convinced that we can achieve a turnaround with him."
Thioune began his coaching career with Osnabruck in 2017, leading the club to promotion from the 3. Liga to Bundesliga 2. He later oversaw 188 matches in the second division across spells with Hamburg and Dusseldorf, narrowly missing promotion in 2024 when Dusseldorf lost a play-off to Bochum on penalties.
"I'm very much looking forward to working with the team and I am convinced that we will achieve the club's goals," Thioune said. "After the very positive discussions with the management, it quickly became clear to me that I wanted to join Werder."
Thioune has already led his first training session and faces an immediate challenge, with Bremen visiting Freiburg this weekend before hosting champions Bayern Munich in his first home game in charge.