The 72-year-old is claiming that the channel only axed him after almost three decades work solely on the basis of his age - a decision which he claims caused him, "public humiliation, stress and mental anguish."
"After 29 years with Channel 4 Racing, on a rolling annual contract, I have been sacked without any consultation or cogent explanation. I am 72," he said in a statement.
"Ageism is illegal. For tens of thousands of employees it has become the feared scourge of our society. This litigation should prove to be a watershed."
McCririck's TV career began with ITV in 1981 after a long spell working for the Racing Post, and he became part of Channel 4's racing team when the channel first began covering it in 1984.
He is claiming £500,000 damages for loss of earnings, damage to his career and his own anguish.
His also also claiming a further £2.5m in "exemplary, punitive" damages which he says will be, "donated to charitable organisations helping to prevent negative prejudice in the workplace."