Figures from the Great British Tourism Survey also revealed visitors were spending more, with total expenditure reaching Â£1.7bn in Wales.
Tourists were staying longer too, spending on average 3.5 nights in 2014.
And while Wales saw an increase in visitors in 2014, visitors to the UK as a whole were down 7% on 2013.
Ken Skates, Deputy Minister for Culture, Sport and Tourism, said: "These figures are absolutely fantastic and show that Wales is ahead of the game.
"Getting to 10 million visitors is an important milestone and Wales is gaining market share."
The figures were released by Statistics for Wales, while the survey is a national consumer survey that measures the volume and value of overnight trips by UK residents.
More than 10 million tourists stayed overnight in Wales last year - the highest number since 2006.