Gardephe ruled that O'Neill's "on-call" time potentially qualifies for overtime compensation.
O'Neill said she was paid at a flat rate of about $50,000 annually when she was first hired and $75,000 annually the second time by the pop singer, who is estimated in a list published by Forbes magazine to have earned $80 million in the first six months of this year.
Lawyers did not immediately comment.
In his written decision, Gardephe noted that lawyers said Lady Gaga, listed in the litigation under her birth name - Stefani Germanotta - and O'Neill frequently slept in the same bed because O'Neill never had her own hotel room while on tour and was required to address Lady Gaga's needs throughout the night.
O'Neill had testified in a deposition that if Lady Gaga was watching a DVD in the middle of the night and grew tired of it, she woke her up to take out and replace the DVD.
"Every day is a work day for her, so every day is a work day for the rest of us," she said. "There is no, `We're going to stay in, we're going to sleep.' There is no, `Let's put on sweatpants and go out to the movies and be girlfriends.' It doesn't work like that," O'Neill said.
In her deposition testimony, Lady Gaga had testified: "You don't get a schedule. You don't get a schedule that is like you punch in and you can play ... at your desk for four hours and then you punch out at the end of the day. This is when I need you, you're available."
O'Neill had testified she was responsible for sometimes monitoring the singer's email and telephone communications and for handling all her luggage - generally 20 bags - including clothing, accessories, makeup and toiletries.
She was also responsible for making sure that "special food" was available at every location and for making sure the singer arrived at performances on time and had ample time for hairstyling, makeup and voice warm-ups and that she appeared on stage on time, O'Neill said.
She said she assisted with costume changes during performances and was responsible afterwards for arranging ice packs, tea and a shower, along with dinner and an exit from the venue.
The judge noted that the women met after Lady Gaga moved into O'Neill's apartment building on the Lower East Side of Manhattan before 2008, when they became roommates and friends. O'Neill was offered a position as her personal assistant because they were friends and she had experience in the music industry, court papers said.