Mikołaj Mielecki (died 1585) was a Polish nobleman and politician. Since 1569 Mielecki was the voivod of Podolian Voivodship, between 1578 and 1580 he also served in the Polish Army as the Grand Hetman of the Crown.
One of the most notable partisans of the Habsburg faction in Poland, since 1562 he took part in various military campaigns to Moldavia under command of Mikołaj Sieniawski. In 1579 he was the commander of all Polish armies in the war against Ivan the Terrible, Grand Duke of Muscovy. One of his most astonishing successes was capturing the city and the stronghold of Połock. Following various disagreements with Stefan Batory and Jan Zamoyski he resigned his posts and retired from public life.
Initially a lukewarm Calvinist and a member of the Polish Reformed Church, in the late 1570s he converted to Catholicism, with his wife and children following him a few years later.