Principal Sessions Judge Shalini Phansalkar-Joshi convicted the accused - Vijay Jadhav (19), Kasim Bengali (21) and Mohammed Salim Ansari (28) - under section 376(e) (repeated offence of rape) of the Indian Penal Code.
The three were earlier convicted in the gangrape case of a telephone operator at the Shakti Mills compound and sentenced to life imprisonment in that case.
The amended rape charge section 376(e), which came into effect after the 2012 Delhi gangrape case, attracts the maximum penalty of capital punishment.
The court is likely to pronounce the quantum of sentence tomorrow after hearing the arguments.
The court had last month framed an additional charge against the three under section 376(e).
The 18-year-old telephone operator was gang raped on the premises of Shakti Mills in July last year a month before the photojournalist was brutalised on August 22.
The three men have already been sentenced to life imprisonment in that case.
According to prosecution, this qualifies them for punishment under the amended section in the photojournalist gangrape case.
The 22-year-old photo journalist of a magazine was gangraped by Vijay Jadhav, Kasim Bengali, Salim Ansari, Siraj Rehman and a minor boy when she had gone to the Shakti Mills compound in the Central Mumbai with a male colleague on an assignment.
The Bombay High Court had last week refused to interfere with the sessions court's decision to frame a fresh charge for repeat offence of rape.