The Cubs, who open the season in one week against the Milwaukee Brewers, now will have a rotation of Carlos Zambrano, Ted Lilly, Dempster, Rich Hill and Marquis. Jon Lieber, who also was competing for one of the spots, will go to the bullpen as a long man.
"It's a shame we can't have a six-man rotation," Cubs manager Lou Piniella said.
Dempster was the Cubs' closer the last three seasons, and hasn't been a full-time starter since 2002 with Florida.
"Dempster has worked hard and he's thrown the ball well here," Piniella said. "We told him we'd give him every opportunity to start this spring, and we did just that. He came to camp and his mindset was to get a spot in the rotation, he worked really hard and he threw well all spring. Marquis has pitched well, also."
Dempster found out before his start against the Texas Rangers on Monday.
"I'm excited," Dempster said. "I worked really hard this winter, and I'm glad they gave me the opportunity to come back and get a shot at starting."
Dempster didn't have the kind of outing Monday to celebrate the announcement. He gave up four runs on eight hits and three walks over 4 2/3 innings.
"When he gets in a little trouble, he has to get out of trouble," Piniella said. "He prolongs the inning a little bit. I think that's something that has to be ingrained in him again, starting pitching-wise.
"Outside of that, his pitches were crisp," Piniella said. "Here in Arizona, with the heat, and hitters getting sharp, you're going to give up runs. At the same time, I've noticed when he gets in a little trouble, he gets a little too fine. He has to go after the hitters and they'll get themselves out."
Dempster was the Cubs' closer for the last three seasons, and now Kerry Wood has that job. Anything about being the closer that Dempster will miss?
"When you have a rough outing as a starter, five days can't come fast enough," Dempster said. "As a closer, you have a chance to redeem yourself the next day. It's two different parts of the process. I'll miss that ninth inning adrenaline rush."
Neither Dempster nor Marquis had an inkling of what would happen, but neither seemed surprised by Piniella's announcement.
"I've pitched well enough to warrant me being in the rotation," Marquis said. "It has nothing to do with the other guys competing because they threw well this spring, also.
"I worked [hard] all year to come into the season as a starter," he said. "I went out there and proved I still belong, and I can help this team get to where it needs to be."
The Cubs kept the competition fair, even after Marquis made it clear that he wanted to start, and if the team didn't need him, he wanted to go somewhere else.
"There was a little bump in the road, miscommunication between myself and Lou," Marquis said. "We have to turn the page."
Marquis gave up three runs in the first inning Sunday against the San Diego Padres, and then settled down, and retired 11 in a row. The right-hander, who has won 54 games over the last four years, does have a history of fast starts, with a career 43-28 record in the first half compared to 25-33 in the second half.
Cubs pitching coach Larry Rothschild delivered the news. Piniella also talked to Lieber and told the right-hander that this doesn't mean he will never start.
"When this is all said and done, we'll need more than five starters," Piniella said. "That's always the case with every club. No team is lucky enough to get away from that."
Last year, the Cubs used seven starters en route to winning the National League Central, and were careful with pitch counts and tried to give them an extra day, when possible.
"I can totally understand the situation," Lieber said. "I've said from Day 1, those guys have earned it just as much. I think it's a great situation we're in. My hat's off to them. It was awesome to go through that. They worked their tails off and they deserve it just as much."
Lieber was named to the 'pen in Philadelphia, but the news caught him off-guard. This year, he was better prepared.
"It's going to be an adjustment," Lieber said. "I don't think I'm the kind of guy who will come in in the middle of the inning in a tight ballgame. It'll basically be long relief. You deal with what you're dealt and move on."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.