The term "rapier" can be difficult to define. Generally, European swordsman did not categorise swords the way we do.

For example, Fiore dei Liberi, a 14th century master of arms, used the Italian word "spada" for his sword, which was a two-handed longsword, in his treatise on knightly martial arts. Hundreds of years later, 17th century master Ridolfo Capo Ferro used the same word "spada" to refer to a long, one-handed sword with a complex hilt designed mainly for the thrust - what we would probably call a "rapier".

To complicate matters even more, the 16th century German master Joachim Meyer used the word "rappier" to describe a one-handed cut-and-thrust sword, which would be called a "sidesword" by modern HEMA practitioners, based on the Italian term "spade de lato". But Italian masters that taught the use of this weapon, like Achille Marozzo and Giovanni dall'Aggochie simply call this weapon a "spada".

So how does this relate to the question at hand? Well, basically, there were certain swords, sometimes called "military rapiers" by modern people, which were used on the battlefield. If your definition of what a "rapier" is can accept those weapons (a bit more like cut-and-thrust swords and less like the thrust-optimised "rapier" we're familiar with) as rapiers, then yes, rapiers have been deployed in more regimented battles.

So now we have established that for some definitions of "rapier", the weapon did appear on the battlefield. But how effective are they? Now here's the kicker: throughout human history, swords were NOT primary weapons on the battlefield, outside of a few notable exceptions (like the Romans). From antiquity through the middle ages, spears were far more common. European knights? They used lances, pollaxes and other polearms. Japanese samurai? They started out as horse archers, and during the Sengoku period the spear was still the weapon of choice in a set-piece battle. Specifically, for the heyday of the rapier, the main battlefield weapons were the pike and early firearms. Personal sidearms like the rapier rarely enter into the equation at all! So was it ever used effectively? I would say no, in that the use of rapiers was never the deciding factor in the outcome of a battle. But then again, that statement can be applied to about 99% of all swords throughout human history, and while it might not have won or lost a battle, its use did control the life and death of certain individual soldiers on the battlefield, but accounts of those fights are rather harder to find.

TL;DR Depends on what you call a rapier. Some were used in battle, but swords never decided battles anyways.

Sources mentioned:
Fiore dei Liberi, whose work on knightly combat included the use of wrestling, daggers, swords, spears, lances and other weapons.

Ridolfo Capo Ferro, an Italian rapier master.

Joachim Meyer, a German master who taught a whole bunch of different weapons.

Achille Marozzo, a Bolognese master who published a very extensive treatise of arms.

Giovanni dall'Agocchie, another Bolognese master.