Hanover are 16th in the Bundesliga on 17 points after 18 games - ahead only of Nuremberg and Hertha - following three straight defeats and seven league games without a win.
"We are convinced that Mirko Slomka and the team can avoid relegation," sporting director Joerg Schmadtke said on the club website.
"He will also be in charge for the future development of the team," Schmadtke said.
Slomka, 42, who has not worked since being sacked by Schalke 04 in early 2008, will be presented on Wednesday. He had stints at Hanover as a player and then as youth coach in the late 1990s and was assistant coach between 2001-4.
"I am looking forward to the challenge of coaching at home and am convinced that we will improve rapidly," Slomka, who comes from Hildesheim near Hanover, said in a statement.
"The team and I have to get used to each other quickly and get points on Saturday against Mainz."
Bergmann, 50, had replaced Dieter Hecking after three matches of this season but could not sustain the good form of his first two months in charge.
It has been a difficult season for the club after the suicide of goalkeeper Robert Enke in November.
After a coaching stint at St Paul, Bergmann was in charge of the Hanover reserves before taking the top job at a top flight club for the first time this season.
"Andreas Bergmann did good work and managed to guide the team through that terrible phase following the Enke tragedy with great sensitivity," said Schmadtke.
"But the necessary victories that will give us the points to stay up have unfortunately not come," he said.
