The 31-year-old DeJesus, who signed a two-year, $10 million deal this week with an option for a third year, is the first free-agent signing by the new Cubs regime headed by president of baseball operations Theo Epstein and general manager Jed Hoyer.
He batted only .240 in his only season with the Oakland A's after eight seasons with the Kansas City Royals.
"It was a tough year but I learned a lot," DeJesus said. "That's not the player I am. I know that."
His best season came in 2008 with the Royals when he batted .307 with 12 home runs and 73 RBIs. He could be the starting right fielder and is the type of player Epstein likes because he is well-rounded, can hit right-handed pitching, runs the bases well and is a strong defensive player.
DeJesus, whose wife is from Wheaton, lives in the suburbs and has been keeping track of all the hype surrounding the arrival of Epstein and Hoyer.
He didn't know quite as much about new manager Dale Sveum, but took a familiar path to educate himself.
"I went on Wikipedia and looked him up," DeJesus said. "I saw that he had a lot of experience with managers who have won a lot of games."
DeJesus will receive $4.25 million in 2012 and '13, and the team has a $6.5 million option for 2014, with a $1.5 million buyout.
Information from The Associated Press was used in this report.