Ms Geoghegan (22) told the association executive last weekend she was giving two weeks' notice to pursue personal goals.
She was "excited personally" about what lay ahead, and would be flying to Brisbane next week, before taking up a tourism-related job involving a Victorian skifield, she said in an interview yesterday.
She would also do some travelling within Australia before returning to Otago University and continuing her law and BCom marketing studies in the second semester.
Ms Geoghegan, who had been serving her second annual term as president, knew there had been some criticism about her departure, given the imminent prospect of the VSM Bill, to introduce voluntary student membership of students associations, being enacted.
"OUSA is not an organisation that revolves around me," she said.
The association had a strong team of paid staff and student executive members which was "more than capable of carrying on" its work.
OUSA had long been preparing for the introduction of VSM.
The aims she had set herself to achieve as president, including cutting the association executive from 17 members to 10, and introducing online voting for association policy making, had already been achieved.
She had every confidence in administrative vice-president Brad Russell, who will serve as acting president from next week until a presidential by-election is held.
The death, in a motor accident, of her close friend and fellow Otago marketing student, Scott Ridley, near Hampden on March 31, had not resulted in her resignation but perhaps "puts things into perspective".
When she later heard that a job relevant to her marketing interests was available in Australia, she had decided to take it.
In her resignation letter, Ms Geoghegan said her OUSA involvement had been the "most challenging" and "most rewarding" period of her life.
It was now time for someone else to "take up the wonderful opportunity that this role provides", she wrote.
Former association president Simon Wilson said the the resignation came at an awkward time for the association, given the imminent onset of VSM, and the recent departure of some association senior office staff, including the general manager.
It would take some weeks to hold an election and could take a new president several months to fully get up to speed with the job, at a key time for the association, Mr Wilson said.
Association officials said the cost of holding a presidential by-election would be relatively minor, well under $2000.
No decision about an election date had been made, but with first semester examinations starting on June 8, and the need to avoid disrupting exam preparations, an election might not be held until the second semester began in July, officials said.