It is understood the BBC will be a launch client, along with a number of international companies.
Steel explained that his business offering would be a mixture of reputation, issues management and crisis comms: 'My big theme is that it's better to look at company processes and how they operate to see if you can stop big issues happening in the first place. Many companies are interested in that.'
Steel, who leaves the BBC at the end of this month, added that he had not yet decided on a name for his company.
His client list has been developed over the past six months while he took up a number of speaking opportunities in the Asia-Pacific region.
Steel will not be directly replaced at the broadcaster. Head of press and media relations Paul Mylrea will continue to oversee media once Steel has gone. Mylrea said Steel has an 'enormous and justified reputation'.
Steel was head of press and media relations until last April, when he moved to fill the new role of chief comms adviser at the BBC. He was replaced by Mylrea. Ed Williams is overall director of comms.
One BBC insider said: 'The job Donald been doing since last April was to help him in the transition out of the BBC. The BBC has a lot of shared pain with Donald, so it has tried to treat him well.'
Steel spent 11 years as the BBC's chief media spokesman, after working as a local radio producer and presenter. His first PR role was as publicist for The Archers.
During his tenure at the BBC, Steel has handled stories such as the murder of presenter Jill Dando and the terrorist bomb attack on Television Centre in 2001.
It was reported this week that the BBC is considering axing coverage of Formula One and Wimbledon to save money. Lord Patten, who is about to take the role as BBC Trust chairman, said 'all hell will break loose' when the scope of cost-cutting is finalised and made public.