Mauro Icardi had sent Inter ahead in the early stages of the second period, but Simeone's late effort ensured that the points would be shared at the conclusion of a tight affair in Italy's top flight.
Icardi showed razor-sharp reactions to net from close range after seeing his initial header kept out by Marco Sportiello, but the response from Fiorentina was impressive.
Cristiano Biraghi saw a super free kick kept out by Samir Handanovic in the period that followed, before the equaliser came in the latter stages - Simeone thumping home from inside the box after a smart pick-out from Valentin Eysseric.
Both teams had four shots on target during what was a tight match for long spells, and a difficult run of form has seen Inter fall off the pace currently being set by Napoli.
Inter, who are now without a win in their last five in the league, stay third in the Serie A table on 42 points, while Fiorentina sit seventh - just two points off sixth-placed Sampdoria.