The 89-year-old, whose commentary has defined the sport in the UK, has a treatable form of lymphatic system cancer.
"They've caught it incredibly early. It's treatable, the doctors say my condition is mild and I'm very hopeful," Walker was quoted as saying by the BBC.
He will undergo chemotherapy and has cancelled plans to attend the British Grand Prix at the end of this month.
Walker's first broadcast came in 1948 - he worked on all formats of motorsports until becoming the BBC's full-time F1 commentator in 1978, by which time each race was broadcast live.
Even since his retirement he has continued to be active within the sport and has made occasional reappearances for the BBC.