Atlanta traded pitcher Charlie Morton, pitcher Jeff Locke, and outfielder Gorkys Hernandez to receive McLouth from Pittsburgh.
They also optioned Center Fielder Jordan Schafer, who won the starting job in center just before the season began, to AAA Gwinett.
McLouth looks to replace him as the starting center fielder, joining Jeff Francoeur and Garret Anderson in the outfield.
McLouth has been in the MLB since 2005, and had his best season yet in 2008. McLouth finished the season batting .276 with 26 home runs, 94 RBI, 23 stolen bases, and 113 runs scored.
He had his first career All Star selection last season, as well as his first Gold Glove in the outfield.
So far this season, he has nine home runs, 34 RBI, and seven stolen bases while batting .256. McLouth is 27 years old, and will turn 28 in late October.
Glavine started his career with the Braves, playing for them from 1987 to 2002, before joining the New York Mets the following season and playing in New York until 2007.
He was signed last season by Atlanta, but it looks like he and the Braves will part ways once and for all.
Glavine won the Cy Young Award in 1991 and 1998. He is a 10-time All Star, a World Series MVP with the Braves in 1995, and joined the 300-win club in 2007, now having a total of 305 wins.