The 25-year-old Northern Irishman became the first man to stop the 26-year-old Spaniard with a superb right hand in the ninth, which saw Martinez hit the canvas.
The referee gave Martinez the chance to show he could fight on, but it was quickly evident he was unable to continue as he stumbled towards the ropes at the Odyssey Arena and the celebrations began for Frampton's corner.
Frampton looked comfortable in a cagey first round, but Martinez upped the tempo in round two and started to land some body shots on the Belfast fighter.
The contest exploded into life in the fourth round, with a powerful left hook from the Spaniard catching Frampton off-guard.
But the challenger hit back and began to chip away at his opponent before gradually assuming control and ending the fight in style in the ninth.
"It feels amazing," Frampton said on Sky Sports 1. "I just want to thank everyone who came out here. I just want the whole of Belfast to be proud of me. I want to be a world champion and I'm getting close."
The Belfast man played down the pre-fight tension between the pair in his post-match interview.
"(It was a) very tough night. He was harder to hit than I thought. He's tough as nails," Frampton said of Martinez, who made throat-slitting gestures towards his rival at Friday's weigh-in. "All that stuff at the weigh-in - that's just macho-ism. He's a nice guy and I'll shake his hand.
"I told him I'd outbox him at the start and I'd outfight him at the end - and that's exactly what I've done.
"He's a big, big puncher. People had doubts about my chin. It just shows I've got a solid chin. He's one of the hardest fighters in the super-bantamweight division and I could take him all day."