Southwell said the move would organise Atkins around key markets, such as rail, education, health and defence, rather than focusing on the firm's expertise in particular fields. It is currently grouped into property, transport, and management and industry divisions.
He said the new operating businesses would have their own profit and loss accounts and managing directors.
Southwell, who joined Atkins in April from defence supplier BAe Systems, said: "Say there are 15 things we do we very well in our markets; the professional compatibility needs to be channelled into market-led, customer-focused activities. This will ensure that we align ourselves to our chosen marketplace."
He will outline his plans to 120 Atkins managers at a strategic conference today and tomorrow.
Southwell stressed that the move would follow staff consultation. He said: "This approach is inclusive; I really want to drive a radical change in the behaviour of the staff.
"I want the guys to feel able to talk more effectively between each other. This will create an entrepreneurial culture with very, very obsessive businessmen."
He added that the shake-up would not see a slash-and-burn exercise at the consultant. He said: "It's not a wholesale restructuring or rationalisation. The important thing to remember is that this is a successful company."
Southwell said he would also be creating the role of a strategic and commercial director, who will come from outside the industry and will help to implement the changes.
He added that he was looking to add acquisitions to the group's US transport operations.
"There are a couple of businesses we are talking about at the moment. We must ensure that the companies have good management and are balanced businesses."
Southwell said he was looking at businesses offering IT systems that support road and rail projects.
Atkins bought Oklahoma-based consultant Benham for £32m in 1999.
