BOSTON – Gov. Deval L. Patrick last week announced that William “Mo” Cowan, chief of staff to the governor, will leave state government and return to the private sector in January 2013. Brendan Ryan, currently director of communications, will succeed Cowan.

Cowan assumed the role of chief of staff in January 2011 and in that capacity has been “central to every legislative and administrative initiative,” Patrick said in a news release. Cowan has been the governor’s chief strategist and adviser, successfully overseeing initiatives including health care cost-containment law and the Expanded Gaming Act. Patrick also said that Cowan was instrumental to the effort to overhaul the state Parole Board, successfully managing the internal investigation of board conduct and overseeing the selection of replacement board members.

According to a news release, Ryan is the longest-serving member of the governor’s senior staff. He was deputy chief of staff in 2007 and 2008 before taking a leave to work as the Massachusetts political director for Obama for America during the 2008 presidential campaign. Ryan returned to the governor’s office in 2009 as a special adviser. Patrick tapped Ryan to lead the transition in leadership at the Mass. Bay Transportation Authority in 2009.

In 2010, Ryan worked as the deputy campaign manager for Patrick, before returning to the governor’s office as director of communications in 2011. •