The much-anticipated report by scientists at the National Oceanic and Atmospheric Administration (NOAA) was confirmed by an independent analysis from the US space agency NASA that reached the same conclusion.
"Record warmth was spread around the world," said the NOAA report.
"The globally averaged temperature over land and ocean surfaces for 2014 was the highest among all years since record keeping began in 1880."
For the year, the average temperature was 1.24 degrees Fahrenheit (0.69 Celsius) above the 20th century average, beating the previous record-holding years of 2005 and 2010 by 0.07 F (0.04 C).
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Record cold for the year was apparent only in some parts of the eastern and central United States.
Experts said the report offers more evidence that humans are driving global warming by burning fossil fuels that boost harmful greenhouse gases in the atmosphere.
"People are always asking, of course, why do we think this is going on," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in New York.
The research group Climate Central said the odds were one in 27 million that the warming trend -- in which 13 of the hottest 15 years on record have all occurred since 2000 -- could have happened randomly, without human-driven influence on the planet's temperatures.
"What's surprising is that anyone is surprised that 2014 was the hottest year on record. The science has been screaming at us for a long, long time," said Secretary of State John Kerry.