The death of logistics specialist Randall Smith brings to five the number of people killed by gunman Mohammad Youssuf Abdulazeez. The other four victims were US marines.
Abdulazeez was himself later killed in a shootout with police.
The FBI has said his motives for the shooting were unclear.
However, it says it has found no evidence that he was carrying out an international terror plot.
Abdulazeez first fired shots at a recruitment centre in Chattanooga, then drove about six miles (10km) to a Navy and Marine reserve centre, where he shot and killed the marines, and wounded Navy Petty Officer 2nd Class Smith.
"A male Navy Petty Officer succumbed to wounds received in the July 16 shooting at the Navy Operational Support Center (NOSC) in Chattanooga, Tennessee" on Saturday at 02:17 local time (06:17 GMT), the US Navy said in a statement.
It did not name the sailor, but family members confirmed it was Randall Smith.
A relative told the US military newspaper Stars and Stripes that She said Smith was married with three young daughters.
A US sailor has died from wounds sustained in an attack on military buildings in Chattanooga, Tennessee, two days ago, the US Navy says.