The Question Time host said he was hesitant at first about getting the permanent mark, but then decided to "man up" and go through with it.
The tattoo of a scorpion has been etched onto David's right shoulder, and symbolises his star sign Scorpio.
"You are only old once," David told Radio Times. "I have always wanted a tattoo. I thought I might as well have it done now. It's a dream come true for me.
"I'm rather fond of it actually, this little scorpion sitting on my shoulder ready to attack my enemies."
Referring to Cheryl Cole's extensive rose tattoo on her bottom, David said that he "wasn't tempted to have any private parts decorated".
Unlike the criticism Cheryl received on Twitter, some rushed to praise David in his surprising act.
"David Dimbleby. Respect. That scorpion tattoo is the first tattoo that I have ever liked on anyone! #trampstamp," wrote broadcaster Andrew Castle.
"Just found out David Dimbleby has got his first tattoo. The dude is 75. LAD," posted another Twitter user, Jarleth Eaton.
David got the tattoo while making his new maritime series, Britain and the Sea. The television personality was exploring how body art was first introduced to the UK as a result of Captain Cook's South Sea adventures, and was offered the chance to have his own inking done.
At first, the 75-year-old thought he was too old and accepted a "feeble" marking in black pencil instead.
"When I saw it in a preview of the film I thought 'That's a bit feeble,'" said David. "I thought it was wimpish having it just drawn on and I needed to man up.
"It took about 30 minutes — an hour in all — and I thought of Winston Churchill having his done while mine was being done. It wasn't painful at all, it just zings a bit. It's modest."
David added that his wife Belinda was "mildly amused" by it and believed that in the past she had been tempted by having one done.