Plattner's counterpart, Henning Kagermann, will continue as sole CEO, ensuring continuity at SAP after the departure of the last of its original founding members following the next shareholder meeting on 9 May.
Plattner's move follows months of speculation about his future at the company he founded with four colleagues from IBM more than 30 years ago.
"I think it's inevitable," said Bruce Richardson, analyst at industry research group AMR. "The guy's a billionaire. He doesn't have to work as hard or travel as much ... the company's direction has been set. It's settling in to execute well on really modest growth probably for the next two to three years."
"So if you're going to pick a time to retire, you can go out at the top or you can gracefully slip out the back door during a down market," he said.
A successful yacht racer, the 59-year-old Plattner stepped aside from overseeing the group's technological development last month. His exit comes amid a growing perception among observers and analysts that his enjoyment of the job was waning.
He failed to show up for SAP's annual news conference and a meeting with analysts at the end of January after competing in the Cape to Rio yacht race.
No change of course
SAP, which supplies business planning and Web-based e-business software to some 19,000 customers worldwide, has ridden out the global slump in information technology spending better than many of its rivals. It aims to boost both earnings and market share despite the general software gloom.
After enduring an extended period of scepticism at the beginning of the decade, when it was accused by many analysts of having missed out on the Internet, SAP has established itself as one of the world's leading business software makers.
It comfortably beat analysts' forecasts for 2002 results in January, when Kagermann said that SAP was in the strongest position it had ever been, and on Thursday it proposed a 2002 dividend of €0.60 a share, up from €0.58 a year earlier.
"We have everything in good shape, and it just seemed a good time to do it. I don't think that much will change," Plattner told Reuters. "I probably won't be able to shout at people as much."
Kagermann, a former physics professor who joined Plattner as head of the company in 1998, is a well-respected figure whose cool good humour has provided a counterbalance to Plattner's sometimes fiery personal style, and he said the company would continue on course.
"We have to accept that it is now a mature industry but SAP is well positioned and our industry still needs growth," he said. "We have to find the right combination, that's all."
SAP shares closed almost 7% higher, in line with a surging blue-chip DAX index.
In New York, the shares closed up 5.99%, or $1.13, at $19.98 on a day when broader markets rallied. The Dow Jones Industrial average closed up 269.68 points at 7821.75.
Plattner's pugnacious drive and technical strengths helped make SAP one of Europe's most successful companies in the past three decades, and he stands out as one of the most colorful personalities in the German corporate landscape.
Germany's 10th-richest man, according to one recent survey, he has been more than willing to indulge in the verbal rough and tumble tradition in the software industry and has frequently traded digs with US rivals such as Larry Ellison of Oracle or Tom Siebel of Siebel Systems.
Looking back, Plattner said one of his most memorable moments was when he and his partner briefly discussed a customer demand for a discount from one of their first clients, ICI. He quickly decided to turn down the British chemicals giant, illustrating Plattner's considerable self-belief.
But he was also particularly proud of the company's success in the US, the world's biggest software market, where SAP has become the biggest enterprise software provider despite its fair share of sniping from local rivals.
"Not so many European companies have become such big US companies," he said.
While stepping down as CEO will take him out of the direct spotlight, Plattner is thought unlikely to pull back altogether from the software industry.
"He can now be the visionary that shows up at [SAP trade fair] Sapphire and selective customer events and not be constrained that whatever he says is taken down as gospel as head of a $7bn software company," AMR's Richardson said.
"He can still have the visibility that he loves with the same sort of reverence that a Jack Welch or a Lou Gerstner enjoys without working himself to 65 or 70 years old. He can be the senior statesmen of the software market."