Judges in Strasbourg found that the actions of the French government were disproportionate and violated article 10 of the European Convention on Human Rights which deals with press freedom.
"The measures taken were not reasonably proportionate to the legitimate aim pursued, having regard to the interest of a democratic society in ensuring and maintaining the freedom of the press," said the ruling published on its website.
In 2004 French daily L'Équipe and weekly news magazine Le Point printed a series of articles containing tapped transcripts of telephone conservations linked to a judicial investigation launched into allegations of doping among members of the Cofidis cycling team.
French authorities subsequently searched the media offices plus the homes of the five journalists who covered the story to establish how it had been leaked, seizing computer hard drives and documents.
The journalists were released due to a lack of evidence. They later lodged a complaint with the European court in 2007.
France's government "had not shown that a fair balance had been struck between the various interests involved," said the judgement.
"Even if the reasons given were relevant... they did not suffice to justify the searches and seizures carried out."
It noted that the searches could have an impact on the protection of journalistic sources.
"The protection of journalistic sources (is) one of the cornerstones of freedom of the press.
"Interference with the confidentiality of journalistic sources (can) only be justified by an overriding requirement in the public interest," the judgement concluded.