The Cubs will send the Padres a player to be named later as compensation for Hoyer and McLeod.
Byrnes, the Padres' senior vice president of baseball operations, will be announced as executive vice president and GM in a Monday press conference. Hoyer will have a similar title in Chicago, while McLeod will be senior vice president of scouting and player development.
A joint statement issued by the two clubs said that out of respect for the World Series, both clubs agreed to forego further comment until their respective press conferences.
This will be Byrnes' second stint as a GM after he headed up the Arizona Diamondbacks' baseball operations department from Nov. 2005 until July 1, 2010, when he was dismissed along with manager A.J. Hinch.
Byrnes has spent 17 years in baseball working in a variety of roles. In addition to his tenure as GM of the D-backs, he served as assistant GM of the Red Sox and Rockies after beginning his career in 1994 with the Indians.
During Byrnes' time in Boston, the Red Sox won the 2004 World Series, their first title since 1918. While he was with the Indians, Cleveland broke a 41-year playoff drought and won five consecutive American League Central titles.
The D-backs had initial success under Byrnes, winning 90 games and the National League West title in 2007, advancing to the NL Championship Series before losing to the Rockies.
Arizona started out 20-8 in 2008, but finished second to the Dodgers with an 82-80 record.
The D-backs struggled to a 70-92 mark in '09 and Byrnes was dismissed the following season with the team on its way to a 65-97 record.
Byrnes was hired by the Padres in December of that year, reuniting him with San Diego vice chairman and CEO Jeff Moorad, who initially hired Byrnes while he was CEO of the D-backs in 2005.
Hoyer was hired on Oct. 26, 2009, replacing Kevin Towers, who was dismissed during the final days of the '09 season. He stated during his introductory press conference that "my goal is to build a consistent winner, year in and year out, for the city of San Diego."
Hoyer didn't waste time delivering on that goal.
Reading a slow-moving free-agent market, Hoyer picked up two key pieces for the 2010 season -- pitcher Jon Garland and catcher Yorvit Torrealba -- at below-market value. He added utilityman Jerry Hairston on the cheap as well.
Before the July 31 non-waiver Trade Deadline, Hoyer traded for outfielder Ryan Ludwick and shortstop Miguel Tejada, the latter a pivotal acquisition for the stretch run.
The results were a team that, built on the premise of run prevention, won 90 games on a $37 million payroll and wasn't eliminated from the postseason chase until the final day of the regular season.
"To a man, I think they're pretty hungry for next year," Hoyer said after that season.
There figured to be some regression in store for the Padres in 2010, especially following the December trade that saw Hoyer deal All-Star first baseman Adrian Gonzalez -- who the Padres could not have afforded once he became a free agent -- to the Red Sox for four players.
Hoyer landed outfielder Cameron Maybin in a trade with the Marlins, acquired shortstop Jason Bartlett from the Rays and signed pitcher Aaron Harang to a one-year deal, though similar deals for first baseman Brad Hawpe and infielder Jorge Cantu backfield while second baseman Orlando Hudson -- who the team still owes $7.5 million -- struggled.
Instead of adding players at the Deadline for another run at the playoffs, Hoyer was instead a seller this July 31.
Hoyer added three prospects in the Gonzalez deal and two more, pitchers Robbie Erlin and Joe Wieland, when relief pitcher Mike Adams was dealt to Texas.
There were other gains made during Hoyer's two seasons in San Diego. He devoted more resources to player development, amateur and professional scouting and endorsed over-slot bonuses during the two First-Year Player Drafts he presided over.
Steve Gilbert is a reporter for MLB.com. Follow him on Twitter @dbackswriter. Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.