During the news conference Ban heaped opprobrium on those who have attacked him through what he called slander and "fake" news reports.
Although he never officially declared he was running, Mr Ban embarked on a series of public appearances and repeatedly spoke of the need to bring about a "change in politics" in a country where a corruption scandal has seen President Park Geun Hye impeached.
Former United Nations secretary-general Ban Ki-moon said Wednesday that he would not run for president of South Korea, a surprise announcement after weeks of laying the groundwork to run.
Ban said he would "give up my pure aspiration to achieve a change in politics under my leadership".
"I was very frustrated by (some of the political circles') parochial, selfish attitudes and reached the conclusion that it is meaningless to move forward with them", he added.
South Korea has been gripped by political chaos since Ms Park was unseated.
Kim Kardashian's alleged robber dubs heist "irresistible"
Almost all of Kim Kardashian-West's stolen jewellery, excepting her diamond engagement ring, have reportedly been "melted". It detailed the events that took place on the day she was robbed inside her hotel room.
If she is thrown out, presidential elections would have to be held within two months.
She is now on a trial at the Constitutional Court, which will decide whether her impeachment is upheld or if she is returned to power.
There have been massive protests against Park, who will turn 65 on Thursday (February 2), recently with thousands taking to the streets demanding her ouster.
Before taking the top job at the United Nations, Ban was South Korea's foreign minister from 2004 to 2006 and assisted in implementing a policy of engagement with rivals North Korea.
Mr Ban appeared to have significant support early in an unofficial campaign and was at one time the perceived frontrunner, but his approval ratings fell sharply as he faced criticism about his political competence.
Another bribery case involving his brother and nephew has emerged as another dispiriting setback for Ban.