Under Lefebvre's tutelage, the Padres ranked last in the Major Leagues in runs (380) and batting average (.232) and ranked second to last in on-base percentage (.309).
Ready will remain as hitting coach through the end of the regular season, Padres general manager Kevin Towers said in a press release.
"Randy has been a part of our Minor League system for the past six seasons and has helped to develop many of our current Major League players," Towers said. "He will be an asset to our Major League staff and clubhouse."
Lefebvre was hired as the Padres hitting coach on Nov. 3, 2008. He had previously worked as a Minor League hitting consultant since 2006 and had worked with several of the young position players on the team.
Lefebvre previously managed at the Major League level with the Seattle Mariners (1989-91), Chicago Cubs (1992-93) and Brewers (interim, 1999) and compiled a 417-442 (.485) career record.
He has served as a coach for six Major League organizations -- Los Angeles Dodgers, San Francisco Giants, Oakland A's, Milwaukee Brewers, Cincinnati Reds and the Padres.
Lefebvre replaced Wally Joyner, who gave his resignation before the end of the 2008 regular season.
Ready is in his sixth season working in the Padres organization and in his second year as manager of the Portland Beavers. He has a 489-466 record, including a 116-134 mark in Portland.
A former Padres player, he rejoined the San Diego organization in 2004, serving as the manager of Class A Fort Wayne (2004-06) before taking over the reins at Double-A San Antonio in '07.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.