He has not played since losing a World Championship quarter-final to eventual winner Stuart Bingham in April.
"Looking forward to playing the Masters," the 39-year-old wrote on social media.
The former world number one has won 27 ranking events in his career, including five Masters titles.
O'Sullivan recently told BBC Sport: "I am reluctant to give up this easy life I have at the moment which is very enjoyable.
"I am dithering but at the moment I am enjoying life so much I haven't really got the time to practise or give the game 100%."
The Masters begins on Sunday, 10 January, with the final on the following Sunday, 17 January.
Five-time world champion Ronnie O'Sullivan has confirmed he will return to competitive snooker at the Masters at Alexandra Palace in January.