The 3-times champion will be presenting alongside Clare Balding. He will also be joining the team throughout the rest of the Flat season.
The jockey has ridden 47 Ascot winners — including going through the card and scoring 7 in one day in 1996.
He will be combining presenting with riding at Royal Ascot.
The jockey said he was “thrilled” to be joining the team.
“I’ve been talking to Channel 4 about this opportunity for a while as I have always enjoyed their racing coverage and I am delighted to be able to give viewers an insight into the great thrill of our sport,” he added.
Clare Balding added: “Frankie is a great communicator and personality and would be an asset to anyone’s coverage. He’ll bring energy, insight and enjoyment.”
Meanwhile style guru Gok Wan will be taking on the fashion coverage.
However, Channel 4 came under fire earlier this week, after figures it released for the Derby showed a massive drop off from past years.
3.3m people tuned in in 2012 when the meeting was televised by the BBC.
Last year 1.95m watched on Channel 4. This fell to 1.55m on Saturday (7 June).
H&H columnist Ralph Beckett recently suggested that Channel 4’s team needed a revamp.
All 30 races will be broadcast live with coverage each day starting at 1.40pm.