The Monteverdi Choir rehearses in Cambridge. England. The group performed “Orfeo” at the Kennedy Center. (Nick Rutter)

Don’t call it “opera in concert.” That term presupposes an opera that was written for a certain set of conditions and is being performed without them. In the case of Monteverdi’s “Orfeo” — which John Eliot Gardiner, the English Baroque Soloists and the Monteverdi Choir performed at the Kennedy Center Concert Hall on Tuesday night, thanks to Washington Performing Arts — those didn’t apply.

The piece was first performed in a room in Mantua’s Palazzo Ducale in 1607, at a time when opera wasn’t yet an established genre: Jacopo Peri’s “Dafne” from 1598, known as Western history’s first opera, was an attempt to re-create Greek drama rather than invent a new form. That first “Orfeo” performance had costumes, but perhaps not a stage as we know it, and while the number of instruments was specified in the score, their deployment was not.

And don’t call it “early music,” because that term tends to imply a set of quotation marks around something: a historicizing distance. “Historically informed performance” is in any case a happier name for a branch of the field that has become, as Tuesday’s performance showed, as vital and creative as any in the performing arts. Yes, the instruments were original rather than modern, which meant the muted whirr of gut strings, the strident bite of sackbuts (a Renaissance/Baroque trombone), and the plucks and plinks of chitarrone (those long-necked lutes, a variant of the theorbo) and harpsichord. And yes, some of the young soloists’ voices — that of the Eurydice, Mariana Flores, in particular — had that typical straight, slightly reedy, almost folk-singer quality that comes when trained singers perform without vibrato. But putting a label like “early music” on the Monteverdi Choir would be a disservice to their rich, full, vibrant, nuanced sound; you’d want them on any choral program you can imagine.

Now that we’ve established what Tuesday’s performance was not, here’s what it was: a wholly involving evening of drama and music at the highest level, made so collaboratively that the soloists weren’t even credited for the roles they sang, and with such natural ease and energy that when singers broke into dance and the chorus into clapping, it seemed a natural extension of their performance. If only more opera conveyed the sense that song is a normal means of self-expression.

Gardiner was the evening’s creator in more senses than one: he founded both orchestra and chorus (the latter just celebrated its 50th anniversary), and in the course of a long career has remained a leading instigator and ground-breaker in the field of historically informed performance. Dark-clad and slender, a day past his 72nd birthday, he led gently, coaxing out music with long limbs, sometimes perched on a stool but standing for the bulk of the two-hour, five-act, no-intermission performance.

Daunting? No more than a film might be. The seamless flow of the night, indeed, served to emphasize the dramatic arc, and the musical contrasts between, for instance, the pastoral world of nymphs and shepherds aboveground (recorders and harps, sopranos and tenors) with the darkness of the underworld, limned with the eerie inky near-blattings of lower brass and the powerful bass of Gianluca Buratto as ­Caronte, or Charon, reluctant to take a living man across the river into the realm of the dead.

Orfeo itself is a tough role for a tenor, with long solos in every act and the job of playing the most wonderful singer in the world. Andrew Tortise acquitted himself honorably, with a light but firm voice and notable stamina. (His brief memory slip in the fourth act was not worthy of notice except to prove that singers, too, are human, even when they’re playing demigods.) Also worthy of note were Francesca Boncompagni, with a honeyed, clear soprano; Francesca Aspromonte, particularly notable as the messenger bearing the tidings of Eurydice’s death, and the countertenor James Hall. Picking out names from an ensemble perhaps does a disservice to the spirit of collaboration and unity that exuded from a stage that made a night’s performance feel like a true celebration — and a cause for one.

CORRECTION: An earlier version of this review of Monteverdi's "Orfeo" at the Kennedy Center incorrectly indicated the singers in two of the roles. Mariana Flores sang Eurydice; Francesca Aspromonte sang the Messenger.