Conrad I was the fourth of six children of Margrave John I of Brandenburg and his wife Sophia, daughter of King Valdemar II of Denmark. He was 26 years old when, in 1266, his father died and he and his elder brothers John II and Otto IV became co-rulers of Brandenburg.

Conrad went on to rule in the newly acquired Neumark part of Brandenburg east of the Oder River, though he rarely appeared on the political scene. On one occasion, he assisted his brother Otto IV, when they allied with Duke Mestwin II of Pomerelia according to the 1269 Treaty of Arnswalde, occupying the Pomerelian city of Gdańsk and gaining the Pomeranian territory around Rügenwalde.

He died in 1304 and was buried beside his wife in Chorin Abbey. There is an entry in the register at Chorin as follows:

Anno 1304 ist zu Sched (?) gestorben Markgraf Conrad (I.) Churfürst zu Brandenburg und ist allhier begraben.

— Theodor Fontane, Wanderungen durch die Mark Brandenburg^[1]

Anno 1304 Margrave Conrad (I), Elector in Brandenburg died at Sched (?) and was buried here.

Conrad was married to Constance of Poznań (d. 1281), daughter of the Piast duke Przemysł I of Greater Poland. Together they had four children:

• John IV (c. 1261 – 1305)
• Otto VII (d. 1308), Knight Templar
• Waldemar (c. 1280 – 14 August 1319 in Bärwalde)
• Agnes (d. 1329) married in 1300 with Prince Albert I of Anhalt-Zerbst (d. 1316)

• Andreas Thiele: Erzählende genealogische Stammtafeln zur europäischen Geschichte. Deutsche Kaiser-, Königs-, Herzogs- und Grafenhäuser, vol I, part 1, table 223

• Entry in the database of the University of Erlangen