The title was taken from the 1,488 Gallaghers who took part in beating the same record in Donegal in 2007.
Participants from all over the world travelled from their homes to Catletownbere in Cork.
The name O'Sullivan is thought to have originated in Munster from the word súil, meaning eye in Irish.
There are no shortage of Sullivans or O'Sullivans in the world, as is the 3rd most common surname in Ireland and 92nd in The USA, making it an optimal name for this record.
The clan used social media and a created a website to spread the word for the World Record attempt.
Before the attempt began James O'Sullivan, the World Record bid organiser was hopeful stating “We’re going well, we can’t complain – our numbers are looking good if people turn up. Even if half turn up, we’re still going well – we’ve got a great response from Sullivans and O’Sullivans all over Ireland and from much further afield too so it’s looking good."
Jim O'Sullivan had no need to worry as people travelled from as far as Mexico to partake in the event.
Kelly Sullivan, the chieftan of the clan, said "I feel blessed to have grown up as part of the wider Sullivan-O'Sullivan family, we make a team that can't be beat,"
The count took place in phases. First the participants, who all brought proof of their surname, went through turnstiles to get a preliminary count, before they gathered and an official count was made.
It was then announced "With a total of 1,848 the O'Sullivan clan are the new Guinness World Record holders, congratulations."
