Pippa Middleton has become a worldwide star ever since the wedding of her sister Kate to Prince William was broadcast around the world in April last year.
Speaking at the Leveson inquiry into press ethics and standards, the newspaper's picture editor Paul Silva said that there was "no justification" to publish photos of Middleton going about her daily business.
"There is no reason to photograph her when she is out and about doing her own thing," he said.
"At the moment there are nine or ten agencies outside her house [on any given day]. If she goes to get coffee, she goes back into her house, we get 300 to 400 pictures... [but] there is no justification for using them."
Silva did say, however, that pictures of Middleton would be used if she appeared at an event where permission to take photographs had already been granted.
But he was also pushed on why The Daily Mail sent photographers to the house of Chinese actress Tinglan Hong after she gave birth to Hugh Grant's child last autumn.
Grant had to take out a court injunction on behalf of Hong after she was hounded by paparazzi, saying that up to ten people had camped outside her house every day at that time.
Silva told the inquiry that the birth was in the public domain after her agent had confirmed it, while the story was of "great interest" to the paper's readers.
"There was no inclination in that statement that there was a privacy problem or a problem ahead," he said.
"A story breaks, we then go to their home, we ask them to pose up, if they say no we'll move on and go away. It was a major showbiz story of great interest to our readers."
Silva said that it would have been better if Grant had issued an official picture of the child, and claimed the paper's photographer had moved further away from Hong's house after it became clear that she was becoming distressed.
More Leveson coverage:
> Hugh Grant suspects Mail On Sunday phone hacking
> The Daily Telegraph paid source £150k for MPs' expenses story
> Charlotte Church offered coverage deal to sing at Murdoch wedding