The Daily Herald newspaper in Provo, Utah, broke the news last week that CSUB and Utah Valley University would become the newest members of the WAC.
Cal State officials have now made it official.
"CSUB has accepted an invitation from the WAC board of directors to become a member of the WAC effective July, 1, 2013," CSUB president Dr. Horace Mitchell said to loud applause at a news conference.
CSUB, Utah Valley and Seattle University all applied in 2011 to become non-football members of the WAC, but only Seattle University got an invitation. Recent defections have created additional openings in the conference.
The new WAC should have six teams: Idaho, New Mexico State, Denver, Seattle, Utah Valley and CSUB.
Most of CSUB's teams have competed as independents since the school achieved full NCAA Division I membership in September 2010.
The WAC has been bleeding members in the last couple of years. Fresno State, Boise State, Nevada, Hawaii, Utah State, Louisiana Tech, Texas State, UT-San Antonio and San Jose State have all left or will leave for new conferences.
The WAC commissioner told The Denver Post in August that it has become apparent the league is "unlikely" to have enough football members to compete next season. Jeff Hurd said the conference is now emphasizing simply having enough members to remain a Division I non-football league, according to a report from The Associated Press.
CSUB was already slated to join the WAC as a baseball member starting in March. CSUB men's soccer will join the Pac-12 Conference as an affiliate member beginning in the fall of 2013.