"I'm not here on holiday, I'm here to win and score a lot of goals," said the 31-year-old forward who made his debut at home to the San Jose Earthquakes on Saturday.
"I'm excited about the opportunity," Keane told reporters. "I'm looking forward to hopefully bringing a lot of success."
Financial details of his move from Tottenham Hotspur to the Galaxy were not disclosed when the transfer was announced earlier this week but media reports said the fee was about 3.5 million pounds.
Keane, who has won 108 caps for Ireland and notched a record 51 goals for his country, trained with the Major League Soccer (MLS) pacesetters for the first time on Friday.
Wearing his new strip, Keane was flanked by coach Bruce Arena and high-profile team-mates David Beckham and Landon Donovan at a news conference.
The signing of the Irishman means his club now have a trio of world-class players capable of bringing the Galaxy their first MLS championship since 2005.
"As a player you always have expectations and pressure on you. I've had that since I was 17," said Keane who also had spells with Liverpool, Inter Milan, Celtic, Wolverhampton Wanderers, West Ham United, Leeds United and Coventry City.
"It's up to me to accomplish [my targets] and I think I can do it. I played in the Premier League for a long time and I did what I had to do - I felt it was time for a new challenge."
Midfielder Donovan, who enjoyed a successful loan spell with Premier League Everton in 2009, said he was impressed with Keane at training.
"Our job just got easier by bringing Robbie here," Donovan said. "He looked good, looked sharp and I think he's going to fit in well with this team."
Former England captain Beckham said: "We know he's going to score goals. He's scored goals everywhere he's been."
