The Chicago-based IT major, which helps enterprises systematise data-driven decision-making, has its main delivery centre in this tech hub (Bengaluru) and its global clients include 125 Fortune 500 companies.
"Rajaram will take over the role of CEO from Ambiga while institutional investors General Atlantic and Sequoia Capital will continue to remain with the company," said Sigma in a statement here.
The executive swap came four months after Rajaram divorced Ambiga in May.
Rajaram, who holds 25.5 per cent equity stake in the firm, will buy back Ambiga's 25.5 per cent at a price being mutually worked upon as the financial terms were a family matter.
Acquisition of Ambiga's stake will make Rajaram the company's largest stakeholder.
"Ambiga, who immensely contributed to the company, has agreed to support me and will continue to be on the board," said Rajaram in the statement.
Refuting speculation about her starting a competitive firm, Ambiga said she had agreed to support Rajaram's interest in purchasing her shares and get a controlling stake (51 per cent) to fulfil his vision.
"We have built a great company over the last decade. Due to personal circumstances, it is time for me to move on from the management team of the company and do something different," said Ambiga in the same statement.
Though the 11-year-old company raised $30 million in first round in April 2011 from FTV Ventures (FTV Capital), Sequoia invested $25 million in December 2011, growth equity investor General Atlantic joined Sequoia in jointly investing $108 million in February 2013, followed by $45 million from MasterCard.
