Bp chief executive Tony Hayward said he had been "demonised and vilified" over the Gulf of Mexico disaster.
He spoke as his successor pledged to put the oil giant "on the road to recovery" as it reeled under a $32.2bn (£20.8bn) blow from the spill.
The financial hit sent BP crashing $17bn (£11bn) into the red for the April-June period following the Deepwater Horizon tragedy - its first loss in 18 years.
Mr Hayward, who will make way in October for US citizen and fellow board member Bob Dudley, said he had no major regrets about his leadership of the group since 2007, and that his decision to leave was a purely practical one.
He said: "This is a very sad day for me personally. Whether it is fair or unfair is not the point. I became the public face (of the disaster) and was demonised and vilified. BP cannot move on in the US with me as its leader...Life isn't fair."
He added: "Sometimes you step off the pavement and get hit by a bus."
Mr Dudley, who becomes BP's first overseas chief executive, said he did not underestimate the task ahead, but added that BP was "financially robust" and boasted "enviable" assets and staff.
"I believe this combination - allied to clear, strategic direction - will put BP on the road to recovery," he said.
The huge charge includes the direct costs of tackling the spill, clean-up costs for the catastrophe, and a $20bn (£12.9bn) compensation fund agreed in June.
But the longer-term fall-out such as fines, penalties and potential legal action will inevitably add to the bill, and spread the pain over a number of years.
BP also hopes to sell around 10% of its production assets over the next 18 months, with the aim of raising $30bn (£19.3bn) to beef up its balance sheet to meet the crisis.
Meanwhile Mr Hayward, who has drawn fire for a series of PR blunders since the crisis began, leaves with a pay-off of one year's salary - £1.045m - and an £11m pension pot.
BP chairman Carl-Henric Svanberg said the firm was "deeply saddened" to lose him, but said the explosion - which left 11 workers dead - had been a "watershed incident".
"It will be a different company going forward, requiring fresh leadership, supported by robust governance and a very engaged board," Mr Svanberg said.