Sparkes, Scope's acting chief executive since the summer, was confirmed as the leader of Britain's largest disability charity last week.
Scope chair Gerald McCarthy said he was delighted: "Jon has demonstrated his strong commitment to our mission and his leadership and vision are an inspiration. He has achieved considerable improvement to the financial position."
Sparkes would not be drawn on whether the role of chief executive at Scope might be reserved for disabled people in the future.
"It is something that would be considered," he said. "Personally speaking, it would be great if Scope had a disabled chief executive."
Andrew Lee, director of People First, the charity run by and for people with learning difficulties, said the decision was a step backwards.
He said: "We are disappointed that Scope hasn't employed a disabled chief executive. It is going against the flow of the disability movement and will generate concern about Scope's future intentions."
Mary Colley, voluntary coordinator of learning-differences charity Danda, said her organisation was "totally against" the choice of a non-disabled chief executive. "It's a great pity," she said. "If you don't have the condition, how can you understand it?"
A spokesman for the Disability Rights Commission questioned the wisdom of organisations that reserved posts for disabled people. "You are going to cut off a lot of skill and talent if you do that," he said.