RIM’s two co-CEOs – Mike Lazaridis and Jim Balsillie – resigned from their positions with immediate effect over the weekend, appearing to bow to shareholder pressure for a change in leadership at the struggling BlackBerry-maker.

Lazaridis and Balsillie – who were also co-chairmen – are to be succeeded by Thorsten Heins, who has been named President and CEO, effective immediately. A former Siemens executive, Heins has been at RIM since December 2007, becoming COO (product and sales) in August last year.

"There comes a time in the growth of every successful company when the founders recognise the need to pass the baton to new leadership,” said Lazaridis. “Jim and I went to the Board and told them that we thought that time was now.”

“With BlackBerry 7 now out, PlayBook 2.0 shipping in February and BlackBerry 10 expected to ship later this year, the company is entering a new phase, and we felt it was time for a new leader to take it through that phase and beyond," he added.

Lazaridis – who founded the firm in 1984 – will become Vice-Chair of RIM’s Board and Chair of the Board’s new Innovation Committee. As Vice Chair, he will “work closely with Mr. Heins to offer strategic counsel, provide a smooth transition and continue to promote the BlackBerry brand worldwide.” Balsillie will stay on as a member of the Board.

Lazaridis and Balsillie have found themselves under increasing pressure to resign in recent months as RIM’s share price has plummeted, leading for calls for the company to be either sold or broken up. Last year, the firm also suffered the ignominy of a high-profile network outage and a major product flop with its poorly-received PlayBook tablet.

Against this backdrop, some major shareholders have questioned the wisdom of having Lazaridis and Balsillie as both co-CEO and co-chairmen and called for a governance overhaul.

In an effort to address these criticisms, RIM named Barbara Stymiest, formerly a member of Royal Bank of Canada’s Group Executive and a member of RIM’s Board since 2007, as the new independent Board Chair. Prem Watsa, CEO of Fairfax Financial Holdings, was also named as an independent director on the Board, expanding it to 11 members.

Meanwhile, new CEO Thorsten Heins appeared to dismiss any thoughts of a sale or break-up of the firm, instead talking up its “strong foundations for growth.”

“We have a strong balance sheet with approximately US$1.5 billion in cash at the end of the last quarter and negligible debt,” Heins said. “We reported revenue of US$5.2 billion in our last quarter, up 24 percent from the prior quarter, and a 35 percent year-to-year increase in the BlackBerry subscriber base, which is now over 75 million.”

He added that RIM was also in the process of recruiting a new Chief Marketing Officer to “work closely with our product and sales teams to deliver the most compelling products and services.”