Hanson, 29, pitched five seasons in the major leagues, four with the Braves and his last with the Los Angeles Angels in 2013 following a trade.
Hanson had been in a coma, according to multiple earlier reports.
A source told WSB-TV, the ABC affiliate in Atlanta, that Hanson had trouble breathing early Sunday morning and was taken to a local hospital. He suffered catastrophic organ failure, multiple sources told the TV station.
Hanson was selected by the Braves in the 22nd round of the 2005 draft and once was considered the top prospect in the organization.
However, after posting a 2.89 ERA over 21 starts in his rookie season of 2009, Hanson slipped each season thereafter. He had a 3.33 ERA over 34 starts in 2010, a 3.60 mark in 22 starts in 2011, a 4.48 ERA in 31 starts in 2012 and a 5.42 ERA in 15 outings (13 starts) in 2013. He saw a gradual decline in his velocity and dealt with shoulder issues that kept him on the disabled list in 2011.
He was 49-35 with a 3.80 ERA for his career.
Information from ESPN.com’s Doug Padilla was used in this report.