He was dropped when the station unveiled its new presenting team headed by Clare Balding.
The presenter said he was taking action in a bid to stand up for others who fear losing their jobs because of their age.
The 72-year-old 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."
He said he was taking action "for loss of future earnings, unfair career-damaging public humiliation, stress and mental anguish".
He said part of the money would be donated to "charitable organisations helping to prevent negative prejudice in the workplace".
McCririck added he would drop the action if he is reinstated, receives an apology and his costs are met.