Sources said her time as acting commissioner following the resignation of her predecessor Martin Callinan in 2014 would help her qualify for a full pension.
She is entitled to a full commissioner’s pension after three years.
As Commissioner, Ms O’Sullivan was on a salary of €180,613 a year.
Now that she has decided to retire, she is entitled to 150pc of her final salary, capped at €300,000, as a lump sum, plus a basic pension of 50pc of her salary.
In her statement announcing her retirement, Ms O’Sullivan said she had been encouraged by international colleagues to apply for the top job with Europol during the summer.
She said that, because it would have been a prestigious appointment for an Irish citizen, she agreed to consider it. However, she said ultimately she decided not to apply for it.