His term begins in November 2016.
Braynon was selected for the role by a unanimous vote of the Senate Democratic Caucus on Wednesday.
"The unity of this vote speaks to the unity of this caucus,” Braynon said in a statement. "And it is that united front that will enable us to do great things for the people of Florida."
Braynon will succeed current Senate Democratic Leader Arthenia Joyner, D-Tampa.
Joyner called Braynon a "true champion for the people."
Braynon served in the Florida House from 2008 until 2011. He is a graduate of Florida State University and a member of Kappa Alpha Psi Fraternity, Incorporated.
Florida Democratic Party Chair Allison Tant said Braynon had "more than earn the trust of his colleagues — he has won the confidence of countless Floridans to fight for them."
"Under Senator Braynon’s leadership, I know the caucus will continue to fight for the values we all share: expanding opportunity, strengthening our schools, and working to grow Florida’s middle class," Tant said.