While most people would be scoffing cake, the TV presenter and author took part in the Royal Parks sponsored run in London which started at 9am (12 October).
Mum-of-one Katie was raising money for her own charity, The Katie Piper Foundation.
She ran the 13.1 miles (21 kilometres) in an impressive two hours and 25 minutes. Her sister Suzy also took part for the good cause.
Sharing a picture of herself before the run with her seven-month-old daughter Belle, Katie wrote: "About to join the start line of The Royal Parks Half Marathon! Have my biggest supporter with me!"
After running the gruelling distance, she tweeted: "Completed birthday half marathon! thank u 2 all who ran 4 @KPFoundation today, congrats to u & my sis @SuzyPiper Hope u all don't ache 2mrw."
Katie founded her own charity after suffering horrific burns in an acid attack in 2008. She has since been working tirelessly to help improve the lives of fellow burns victims.
Katie, who has a new autobiography out called Beautiful Ever After, also got a few birthday treats on her special day.
Posting pictures of a card and a personalised mug, she wrote: "My first mummy birthday card!
"Look what my daughter made me for my birthday! Clever little bean :)."
After her morning workout, we hope Katie got a delicious birthday cake, too!
Happy birthday Katie!
If you'd like to sponsor Katie Piper, click here.
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