Channel 4 deny ageism claims
McCririck was one of a number of faces dropped from the presenting team after Channel 4 awarded the production contract for its racing coverage to IMG Sports Media, ending its previous agreement with Highflyer.
McCririck was vocal in his criticism of the decision when it was announced last October and has decided to pursue Channel 4 and IMG Sports Media through the courts.
However, 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."
In a statement McCririck said: "Channel 4 and production company IMG Sports Media were yesterday each served a letter before action for age discrimination.
"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.
"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."
McCririck said he was being represented on a no-win no-fee basis by employment and sports law specialist solicitor Stephen Beverley, of the London West End Cavendish Legal Group.
McCririck said his solicitor had served papers on the executives he says are responsible for his sacking.
He alleged they are Channel 4's chief executive David Abraham, the broadcaster's creative officer Jay Hunt, sports editor Jamie Aitchison and Carl Hicks, executive producer of IMG Sports Media.
The veteran presenter said: "Mr Beverley is insisting on full disclosure of all documents, phone records and emails up to the present day that led to, and followed, my dismissal.
"My legal team will also be calling past and present Channel 4 Racing presenters and production staff, media executives, journalists and others to be cross-examined in public by my QC, who is also acting no-win no-fee."
McCririck admitted the legal action will have its consequences.
"It won't be pleasant, the vitriol will hurt," he said.
"Some is bound to stick and further threaten my future prospects.
"But that is the inevitable price when asserting what is right against entrenched powerful interests.
"Along with my legal team, I believe this landmark action will be a beacon to motivate numerous workers still productive as ever, but now living in dread of being unjustly axed."
McCririck said he would drop the legal action if he is "fully" reinstated, receives an apology from Channel 4 and all his costs are met.
IMG Sports Media assumed production control on January 1, with former BBC racing presenter Clare Balding and Racing UK anchorman Nick Luck heading up the new team.
Carrigeen Lonicera galloped her rivals into submission with a convincing win in the concluding bumpers for the Lalors.