Messi, 34, helped his country win the Copa America, his first international honour, and has scored 40 goals in 2021 - 28 for Barcelona, four for Paris St-Germain and eight for Argentina.
Bayern Munich and Poland striker Robert Lewandowski came second, Chelsea and Italy midfielder Jorginho was third and Real Madrid's French striker Karim Benzema finished fourth.
The Ballon d'Or is voted for by 180 journalists from around the world, although there was no award in 2020 because of the coronavirus pandemic.
Either Messi or Cristiano Ronaldo (five wins) collected the award every year from 2008 to 2019, apart from in 2018 when Croatia midfielder Luka Modric won it.
Messi had already won the trophy more times than any other player and his seventh success comes after wins in 2009, 2010, 2011, 2012, 2015 and 2019.
"It's incredible to be here again," he said at the ceremony, held at Paris's Theatre du Chatelet.