There was still 45 minutes to go in their own game but closest challengers Atletico Paranaense went down 2-1 at Criciuma in an earlier match and Cruzeiro knew they could not be caught at the top.
Thousands of fans took to the streets in the club's home city of Belo Horizonte, while players danced round the field in celebration.
"It's hard winning the Brazilian league, there are a lot of good teams," said a jubilant manager Marcelo Oliveira. "We worked hard and we were all in this together, and there was a great spirit in the side day in, day out.
"Our numbers were expressive and I'm very happy."
Cruzeiro were particularly dominant during the second half of the season and became the only champion to beat every other team in the league at least once.
They were also the first club outside the traditional hotbeds of Rio de Janeiro and Sao Paulo to win the Serie A since they themselves won it back in 2003.
They have so far scored 72 goals in 34 games, 19 more than any other team, and have a goal difference of +42, more than the next six teams combined.
"We've been united, we work hard, and we are serious about how we go about things," midfielder Willian said of the key to their success after beating Gremio 3-0 last week. "We're all playing well and enjoying a good phase."
One of the most surprising aspects of their campaign is the lack of a truly world class player, Tostao, a former Cruzeiro player and now a newspaper columnist with Folha de S.P., wrote last month.
Although goalkeeper Fabio has excelled and midfielder Everton Ribeiro is the odds-on favourite to win player of the year, it is teamwork rather than individual brilliance that has marked their season, Tostao said.
"The team's real star is their teamwork," he wrote.
"Without forgetting to mark, they score all kinds of goals, from the right, from the left, through the centre, in the air, on the ground, with one-twos, triangles and long balls, from shots inside and outside the box.
"And they don't depend on one goalscorer."
Tostao also paid tribute to coach Oliveira, who was a controversial choice with fans when he took over in January courtesy of his historical links with city rivals Atletico Mineiro, whom he both played for and managed.
But he soon got fans on his side and has now lost only five of his more than 60 games in charge.
"Marcelo used his squad very well," Tostao wrote.
"He substituted and rested players at the right time. Even when they were being taken off for tactical reasons, he led the players and the press to believe he was resting the player.
"I haven't heard of any discontent among the squad."