Country music legend Merle Haggard has died after battling double pneumonia ... according to his manager.

Haggard was diagnosed with pneumonia last year and spent 11 days at the Eisenhower Medical Center in Rancho Mirage early this year. He died at home near Redding, CA on Wednesday morning.

He'd been battling back from the illness and even scheduled a string of concert dates with his pal Willie Nelson. They released an album, "Django and Jimmie" last year.

But last week Haggard canceled his shows for the month of April due to his continuing efforts to recover. His manager tells us Merle was weary from battling pneumonia for so long ... and had even predicted to friends he would die on his birthday.

He was inducted into the Country Music Hall of Fame in 1994.

Merle turned 79 today.