McCririck said he was sacked from Channel 4 Racing in October "without any consultation or cogent explanation".
He is suing Channel 4 and IMG Sports Media, which took over production of the broadcaster's racing coverage from the start of 2013, for £2.5m in punitive damages and seeking a further £500,000 in compensation for loss of future earnings, unfair career damaging, public humiliation, stress and mental anguish.
McCririck was one of a number dropped from the presenting team after Channel 4 awarded the racing production contract to IMG Sports Media, ending its previous agreement with Highflyer.
Channel 4 has expanded its racing coverage after picking up the rights to events previously covered by the BBC, including the Grand National and the Derby.
The broadcaster hired Clare Balding, the BBC's main horse racing presenter, to anchor its coverage.
"Channel 4 and production company IMG Sports Media were yesterday each served a letter before action for age discrimination," McCririck said.
"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.
"For loss of future earnings, unfair career damaging, public humiliation, stress and mental anguish, I will be seeking £500,000," he added.
"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. There's no upper limit to the amount of damages employment tribunals can award under the Equality Act 2010.
"I am seeking a further exemplary, punitive £2.5m, part of which will be donated to charitable organisations helping to prevent negative prejudice in the workplace."
A Channel 4 spokesperson said: "We are grateful to John McCririck for his contribution towards the success of Channel 4 Racing over many years. However, we reject the suggestion that discrimination on the basis of age played any part in the decision not to renew his freelance contract and we will be vigorously defending this claim."
Article from The Guardian