Gerrard will link up with Galaxy once his Liverpool contract expires at the end of the 2014-15 Premier League after signing an 18-month deal with the MLS champions in January.
The 34-year-old former England international - a Designated Player - is expected to play a key role for Bruce Arena's men but that will not involve wearing the captain's armband.
Republic of Ireland international Keane has no intention of relinquishing the captaincy, having led the team since 2013.
"He is arriving as an addition, not as a replacement as captain," Keane told reporters in Dublin.
"I have spoken to Steven and he is excited about the challenge of coming to LA Galaxy. He is going to be a great addition to our squad."
Galaxy kick-off their championship defence against Chicago Fire at Stubhub Center in Carson on March 6.
