After summing up the two days of "contradictory" evidence, Berkshire coroner Peter Bedford said he could not prove beyond all reasonable doubt that the businessman either took his own life or was unlawfully killed.
The body of the former Kremlin insider was discovered slumped on the bathroom floor at his ex-wife's luxury property in Ascot, Berkshire, with a ligature wound to his neck on March 23 last year.
Mr Bedford told the inquest at Windsor Guildhall: "I am not saying Mr Berezovsky took his own life, I am not saying Mr Berezovsky was unlawfully killed.
"What I am saying is that the burden of proof sets such a high standard it is impossible for me to say."
Members of the Berezovsky family declined to comment on the verdict as they left the court.
The inquest heard Mr Berezovsky had often spoken of suicide and became a "broken man" after losing a multibillion-pound court battle with football club owner Roman Abramovich in 2012.
The former Kremlin insider, who fled Russia after falling out with the government, fell into a deep depression as he faced financial ruin and the loss of his reputation after the judge found in favour of Mr Abramovich over a £3 billion debt.
The coroner said: "It is clear to me and the witnesses I have heard from that it had a significant effect not only on his finances but also on his mental health."
Although there were suggestions that the 67-year-old - who had survived at least two assassination attempts - was murdered, police did not find any evidence of foul play.