The right-hander was named as the No. 3 starter, following Ryan Dempster and Matt Garza. Chris Volstad and Paul Maholm round out the starting five.
"This could be right up there," said Samardzija, who has pitched primarily in relief for the Cubs since he was drafted in 2006. "It's definitely at the top because I feel I went through college and I just played. It was natural and I didn't have too many setbacks. I didn't play much freshman, sophomore year because I was 185 pounds.
"I didn't have too many things that I've really had to earn and I had to earn this and it feels good," he said. "To put that work in and see it pay off, it's pretty nice."
Samardzija had a strong spring with the exception of one outing against the Rockies when he gave up seven runs on 10 hits over four innings. On Wednesday, he faced the Indians and threw six scoreless innings, giving up three hits. Cleveland did the same as Colorado, and overloaded the lineup with left-handed hitters.
Cubs manager Dale Sveum and the front office met after Wednesday's game to finalize the roster decisions.
"I'd say it convinced me more than anything," Sveum said of Samardzija's outing vs. the Indians. "He did a good job yesterday, especially because they had seven or eight left-handers in their lineup, which is always a test against any right-handed pitcher. He kept them off balance, got weak popups. That shows he was controlling bat speed and doing a good job of it."
On Thursday, Samardzija was called into Sveum's office to get the news.
"We just kind of said thanks to each other, for me personally to get the opportunity to do it and they were happy I didn't take it for granted and just show up and go through the motions," Samardzija said. "It felt good."
The 27-year-old pitcher has grown up quite a bit in the last few years. He admitted to having a sour taste after previous Spring Trainings when he was either demoted or assigned to the bullpen.
"You don't know how many opportunities you're going to get to start," Samardzija said. "Once you become a reliever and have success, a lot of times that's where you end up in your career. I really wanted to give this a full head of steam and a full shot."
In past years, Samardzija might have had a different approach in Wednesday's game.
"I think that showed my growth and where I'm at today," he said. "Normally, I probably would've tried to throw 100 [mph] and try to strike everyone out and I didn't do that. I came out and threw strikes and continued what I've been doing all spring. I think it shows a little maturity on the mound."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.