The 31-year-old was a free agent after his contract at West Brom expired.
"We are pleased to have been able to bring in Keith early in the transfer window as there were a number of clubs interested in signing him," manager Owen Coyle told Bolton's official website.
"He is highly experienced both in domestic and international football and he will bring strength, competition and a goalscoring threat to our midfield."
Andrews agreed a short-term deal at The Hawthorns in January having arrived on a free transfer from Blackburn, making 14 appearances and scoring twice.
He started all three of his country's games at Euro 2012, seeing red in the final Group C game against Italy.
Wanderers crashed out of the English top-flight on the final day of the league season after a 2-2 draw at Stoke.
Source: AFP
Source: AFP