The number of people following the denomination has increased from just 5% in 1970 to more than 22% in 2010.
There are two main candidates, incumbent Catholic President Dilma Rousseff and Pentecostal Christian Marina Silva.
If evangelicals decide to back Ms Silva, it could swing the election her way and be the first time in years a Catholic has not led Brazil.
Current opinion polls say that is very likely to happen.
Ms Silva has spoken of her faith several times on the campaign trail and even suggested she uses the Bible to influence policy decisions.
It is also the first time two evangelical Christians have stood for election, with pastor Everaldo expected to come third.
The vote is on 5th October 2014. If none of the candidates win 50% of the vote, a second round will take place on 26th October.