The Daybreak showbiz editor and presenter was reportedly approached by producers in the hope that he would provide some comic relief.
"He will be our Strictly clown this year and he is happy to play that role," a source told The Sun.
"Russell Grant was a huge hit on Strictly last year and we are hoping that Richard will attract the same fans. He is hilarious and during meetings had everyone in stitches with his camp jokes.
"He is a great signing for us - we're delighted to have him on board."
Arnold confirmed his appointment on Daybreak earlier this morning (September 7).
The source added: "Richard is well up for the show and Strictly's producers hope he will promote it to viewers of Daybreak.
"But it will mean they also end up promoting Daybreak on Strictly - which has far more viewers."
Tracy Beaker star Dani Harmer has also been confirmed as a contestant for Strictly.
The upcoming tenth series will premiere at 6.30pm on Saturday, September 15 on BBC One.
Watch the trailer for Strictly Come Dancing below: