Lawyers for the 25-year-old contacted the Press Complaints Commission (PCC) about a photograph which appeared in yesterday's Daily Mirror.
The image showed Miss Middleton, wearing sunglasses, walking along clutching a takeaway cup and her car keys.
It is believed to be the first picture used by a newspaper of Miss Middleton on her way to work since she encountered a media scrum outside her flat on her birthday in January.
It is her first official complaint to the press watchdog.
A source close to Miss Middleton was quoted as saying: "Over the past few days she has had some serious aggression from them [photographers]. She has been chased all over the land t every moment of the day, both on foot and in cars."
The PCC said the complaint, which alleges there has been a breach of Clause 4 (Harassment) of the Code of Practice, would be investigated in the normal way and no further statement would be made until the matter had been dealt with.
A spokesman for the Daily Mirror, which is owned by Trinity Mirror, said: "We will provide the necessary thoughts and comments to the PCC. We will not be commenting any further at this stage."
Miss Middleton is represented by Gerrard Tyrrell of Harbottle & Lewis, who also acts for the Prince of Wales. At the start of the year, the firm wrote to the PCC saying they had "disturbing" film of photographers intruding on Miss Middleton's privacy.
Tim Toulmin, the PCC director, said at the time that the letter, which he forwarded to newspaper editors, was a "final warning".
When Miss Middleton ran the gauntlet of press outside her home on her birthday, her lawyers attempted to use persuasion rather than legal action to protect her and the attention appeared to subside.
News International introduced a self-imposed ban on using paparazzi pictures of Miss Middleton, which affects the Sun, the News of the World, the Times, the Sunday Times and free newspaper thelondonpaper.
Royal aides revealed Prince William wanted "more than anything" for photographers to stop harassing Miss Middleton.
His concerns follow the death of his mother Diana, Princess of Wales, who was being pursued by paparazzi when she was killed in a car accident in Paris in 1997.