The first confirmed exoplanet detection was announced in 1992.
Radio astronomers Aleksander Wolszczan and Dale Frail reported two planets orbiting the millisecond pulsar PSR B1257+12 on 9 January 1992. They detected the planets indirectly by measuring regular variations in the timing of the pulsar’s radio pulses. The planets were later joined by a third confirmed world in the same system.
This discovery was surprising because a pulsar is the extremely dense remnant of a stellar explosion. The planets may have formed from material left after the supernova, or they may represent surviving cores of earlier planets. Their existence demonstrated that planetary systems could arise in environments very different from the Solar System.
The date is sometimes confused with 1995, when Michel Mayor and Didier Queloz announced 51 Pegasi b. That was the first confirmed exoplanet orbiting a normal main-sequence star and helped launch modern exoplanet astronomy. Earlier claims, including a 1988 candidate around Gamma Cephei, were not confirmed until much later, so they do not replace 1992 as the standard answer.