McCririck was one of the channel's presenters to be axed when it switched production teams from Highflyer to IMG in 2012.
Derek Thompson, Mike Cattermole and Alastair Down were also dropped in the handover. Veteran form expert Jim McGrath has remained on the team, alongside new anchor Clare Balding.
McCririck spoke out about Channel 4's decision last October and is now suing the channel with the services of employment and sports law specialist solicitor Stephen Beverley, of the London West End Cavendish Legal Group.
In a statement, the TV star 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 is a divisive personality with a unique and boisterous presenting style, who famously appeared twice on Celebrity Big Brother when it was on Channel 4.
Speaking about the changes to the racing lineup last year, a Channel 4 rep said: "It hasn't been an easy process and there have been complications on the way but, with regards to the choice of the squad, we were conscious that the programme will have a very different feel.
"Behind Clare Balding as lead presenter and Nick Luck in a supporting role, we were looking for a more journalistic approach to the content."
From 2013, Channel 4 Racing will be the new home of horse racing on TV. It will broadcast 88 days of coverage a year and show nearly 300 hours of live action.
This includes a range of premium events, including the Cheltenham Festival, Aintree's three-day John Smith's Grand National meeting, the Investec Derby Festival from Epsom Downs, Royal Ascot and Glorious Goodwood.