She took to Instagram to announce the arrival and reveal the gorgeous name.
“Welcome Arnold Martin Kavalee,” her caption read.
Her post garnered plenty of congratulatory well-wishes from fans.
But don’t expect the TIFFXO fitness program founder to go rushing back to the gym now that she has given birth.
"There’s a lot of effort that goes in to the bounce back,” Hall told News.com.au last month.
“Hours at the gym and calorie restrictions. I’m not up for sacrificing time with my new baby to be pumping it out at the gym.
“My body has changed, and that’s all right. I have put on weight, but it’s beautiful, glorious weight.”
Earlier this year she revealed to Kidspot that she was going through extreme morning sickness through her first trimester.
“I’ve been to hospital twice because I’ve tried to continue to work, filming TiffXO and doing the work outs and [I] just kept getting very dehydrated and still having morning sickness," she said.
Tiffiny and Ed, who stars on Channel 10’s Have You Been Paying Attention?, have been married for three years.
Little Arnold isn't the first Biggest Loser baby. Fellow former trainers Michelle Bridges and Steve "The Commando" Willis welcomed a son, Axel, in December of 2015.