Occidental Petroleum shareholders in a vote on Friday ousted Chairman Ray Irani, who had led the company for more than two decades.
CEO Steve Chazen announced the news at Occidental's annual shareholder meeting.
It was a jarring corporate end for Irani, who planned to retire from the Los Angeles-based company next year.
The Wall Street Journal said in March that Irani had pressured Chazen to leave but that the CEO had the support of several big investors. The company denied any friction at the top.
"The announcement was basically a formality at this point," said Allen Good, an oil company analyst at Morningstar in Chicago, referring to Irani's departure. "Ultimately this clears the path for Chazen to continue what he is focusing on so far, which is cost improvement. It also might clear the way for the breakup of the company. ... It might make sense to create a couple of different companies out of Oxy."
(Read More: Commodity Super Cycle Is Dead: Citi)
Shares of Occidental rose nearly 3 percent to $90.51 in afternoon trading on the NYSE.
Taking over as CEO in 1990 from tycoon Armand Hammer, who built Oxy over three decades, Irani oversaw further dramatic growth but raised eyebrows with his lavish pay packages.
Chazen, 66, took over from the 78-year-old Irani two years ago, having served alongside him in the executive suite since 1994.
(Read More: Possible US Budget Fix: Sell Our Strategic Oil)
Occidental said in mid-February that it was seeking a replacement for Chazen. It said in April that the executive would continue in his role through 2014, a move aimed at reducing uncertainty over succession plans.
Earlier this week, influential advisory firm ISS had reaffirmed its recommendation to vote against Irani and for the executive compensation plan, calling recently announced policies a move in a "positive direction."