He was the son of the Palatine of Podlaskie Voivodeship Stefan Mikołaj Branicki and Katarzyna Scholastyka Sapieha, the daughter of Hetman Kazimierz January Sapieha. The first one was the daughter of Court and Grand Marshal Karol Stanisław Radziwiłł, Princess Katarzyna Barbara Radziwiłł, that he married on 1 October 1720 in Biała Podlaska.
One of the wealthiest Polish magnates in the 17th century, owner of 12 towns, 257 villages and 17 palaces. He was the last male representative of the Branicki family. January had three wives.
He was Podczaszy of Lithuania (podczaszy litewski) in 1723, Grand Standard-Bearer of the Crown (chorąży wielki koronny) in 1724, commander of an infantry regiment (szef regimentu pieszego) in 1726, Artillery General of the Crown (generał artylerii koronnej) in 1728, hetman polny koronny in 1735, Palatine of Krakow Voivodship (wojewoda krakowski) in 1746, hetman wielki koronny in 1752 and Castellan of Krakow (kasztelan krakowski) in 1762.
He was the Starost of Brańsk, Bielsk Podlaski, Mościsk, Janów Lubelski, Bohusław, Złotoria, Krośno and Jezierzysk (starosta brański, bielski, mościcki, janowski, bohuslawski, złotoryjski, krośnienski, jezierzyski). Branicki was one of the most powerful and influential magnates in Poland of the 18th century.
He was leader of the magnates party. Connected with the Radziwiłł and Potocki families and an opponent of the "Familia".
He sympatized with confederates of the Radom Confederation and the Confederation of Bar.
Branicki was owner of Białystok. At that time Białystok began to development In 1745 he established a military and engineer school and a theatre.
In 1763–1764 he ran in the election of the King of Poland, but was beaten by his brother-in-law Stanisław Poniatowski.
