The Daily Mail and Daily Mirror had been accused of publishing ''seriously prejudicial'' articles after the serial killer, 43, was found guilty of kidnapping and murdering 13-year-old Milly.
Jurors at the Old Bailey had yet to reach a verdict on attempted kidnapping charges that he abducted 21 year-old Rachel Cowles two weeks short of her 12th birthday.
In June last year she admitted being "extremely hurt and angry" after an Old Bailey jury was discharged without reaching a verdict that Bellfield had tried to snatch her in broad daylight.
Mr Justice Wilkie, the trial judge, had admitted he had been forced into the "deplorable" position of discharging jurors before they returned verdict in the case. The charges will now "lie on the file".
On Wednesday two judges at the High Court in London found the two papers guilty of contempt of court in a case brought against them by Attorney General Dominic Grieve.
Both papers had contested the action.
At an earlier hearing the judges were told the stories were part of an ''avalanche'' of adverse publicity which followed the guilty verdicts against Levi Bellfield while jurors were still deliberating another charge against him.
Sir John Thomas and Mr Justice Tugendhat heard that as a result of the ''totality'' of the publicity, the Old Bailey jury was discharged from returning a verdict on that count.
The charge alleged that the day before Bellfield snatched Milly from a street in Walton-on-Thames, Surrey, in 2002, he attempted to abduct Rachel.
The former nightclub doorman and wheelclamper, who was previously convicted in 2008 of the murders of Marsha McDonnell and Amelie Delagrange and the attempted murder of Kate Sheedy, was found guilty on June 23 last year of Milly's murder.
The newspapers argued that their publications would not have created a substantial risk of serious prejudice. But the two judges ruled in favour of the Attorney General.
The Attorney General said outside court: ''This case shows why the media must comply with the Contempt of Court Act.
''It is unfortunate that the deluge of media coverage following the Milly Dowler verdict, not only by these papers but also other media outlets, led to the judge discharging the jury before they had completed their deliberations on a charge of attempted kidnap, ultimately depriving Rachel Cowles of a verdict in her case.
''This prosecution is a reminder to the press that whilst the jury is still to reach a verdict on all counts of the indictment the Contempt of Court Act applies.
''The question of penalty is now for the court to consider.''