Bates, who has been Tigers promoter for three years, has taken full control of the Lions and will work alongside co-promoter David Darcy.
Bates said: "We're only weeks away from the new season and so our main priority is to quickly form a team.
"We have opened talks with several riders and should be in a position to announce the first signings any day."
Lions endured a miserable season last time out and finished bottom of the Elite League table.
But Bates said he hoped the club's financial difficulties were a thing of the past.
"I am aware that Leicester went through a difficult trading period last season," he said.
"And I will be doing everything possible to ensure that the club is placed on a sound financial footing that secures the future of Leicester Speedway for years to come."
Leicester Lions Speedway have been bought by Sheffield Tigers promoter Damien Bates.