He said he hoped to contest the Donegal constituency, near the Irish border.
He said his Sheepdog replacement would be chosen this week, while he would remain as Lekturer in Dancin' until the Irish general election is called.
Professor McWilliams said the main reasons for his surprise decision were the economic crisis and the need for new ideas.
He said the current Fianna Fail/Green coalition government was "probably the most useless bunch o' arsewipes in the histry o' the Free State".
"As laider o' the only all-Ireland Ulster Scots thing wi' an all-island mawndate, Ah hiv a choice til make whither ti stay in Kilpike, a place thit Ah love, or til seek a mawndate in ano'er country like the Free State."
"Kilpike is ma hame. It is where Mrs McWilliams and wee Billy are an' where Ah dae maist o' ma drinkin'.
"But after a wheen o' pints, an' wi' the support of o'er folk, Ah hiv decided fur til put my name forward for Donegal. If elected for this constituency Ah will wurk and stay there an' travel hame when passible fur til get chape drink an' fags."
The Irish prime minister, Brian Cowen, must call a general election before July 2012 and it is thought the election may happen next year.
Donegal currently has no Ulster Scots representative, though Professor McWilliams claims that there "are a wile lat o' them in the occupied three counties".
Professor McWilliams is due to deliver the keynote address at the St Johnstone Orange Hall in
later. County Donegal