Rowghani was hoping to retain control over Twitter's product vision, operations and corporate development but had to face opposition from Costolo who wanted have more control over those functions, according to people familiar with the matter. Other reports suggest that Twitter's stagnating user growth, seen as one of Rowghani's responsibilities, was the reason for his leaving the company.
Twitter filed an SEC filing saying that Rowghani was leaving the company and that they did not intend on appointing anyone else to the position.
"Goodbye Twitter," tweeted Rowghani. "It's been an amazing ride, and I will cherish the memories."
Twitter went public last November and in its first quarter filing for 2014 the company reported a sluggish six percent growth in active users. Estimates put the total number of active users at 255 million.
Even Twitter's board, which includes founders Jack Dorsey and Evan Williams, have questioned the micro-blogging site's growth in members and user engagement, but still continue to support Costolo.
Rowghani's responsibilities were on the decline after the company hired Daniel Graf as vice president of consumer products. Rowghani wanted Graf to report to him but Costolo decided that the new executive should report to him instead. Costolo also had executives in charge of engineering reporting to him, thereby reducing the need for a COO.
Rowghani is expected to remain at Twitter and and work as an adviser to Costolo.
Despite their reported differences, Costolo tweeted a complimentary message for Rowghani.
"Thank you for being an incredible executive & partner," Costolo tweeted. "Twitter could not have succeeded without you."