The win earned the Sarangani representative the WBO international welterweight championship despite the slow start.
All three judges scored for Pacquiao with 116-110 across the board.
Despite the slow earlier rounds, Pacquiao was eventually able to knockdown Bradley on the seventh and ninth round.
"He's a tough opponent," Pacquiao said in an ABS-CBN News report about Bradley. "He survived the 12 rounds. But I'm not careless. I'm not doing careless (things) in the ring. (I used) the counter punch, the uppercut and the straight, and that was my plan even in training."
Pacquiao added, “Oh yeah, he's different than in the last two fights we had. He improved, that's why it was hard to catch him.”
The fight ended with Bradley ending up with a record of 33 wins, two losses, and one draw, with 13 wins by knockout.
The boxing champ also said he is retiring and focusing on his political career.
Mainphoto courtesy: USA Today Sports images