Qandeel, a prominent opposition journalist, is accused of "insulting and libelling a public servant or citizen performing their work", following comments he made about Egypt's foreign minister, a judicial source said in Cairo.
Qandeel could now face prison or a fine if found guilty.
"Journalists should not have to operate in the shadow of criminal defamation laws, especially those explicitly protecting public servants, whose activities fall within the public interest", Mills said.
"Particularly in a pre-election period it is crucial that Egyptians have free access to a diversity of opinions and news", he added.
Egypt is due to hold presidential elections next year.
Qandeel, who is also a spokesman for a reform group headed by the former UN nuclear watchdog chief Mohamed ElBaradei, said he believed the case was "political."
"This does not have to go to court," he told AFP. "His statements are always criticised in the media. I believe there is a political agenda behind this."
Many restrictions on the independent press in Egypt were lifted in the past decade, but media rights activists say they still face censorship and spurious libel suits.
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