The "Rockstar" rapper took to the stage at the KAABOO Del Mar festival in San Diego, California on Friday wearing a customised airbrushed T-shirt with the words "RIP Mac Miller" across the front, adorned with blue and pink roses.
Malone later shared a photo of himself wearing the custom tee, designed by artist Isa Beniston, on Instagram.
The pair were close friends, and were due to collaborate on an album together before Miller's unexpected death on September 7.
"God f***ing dammit," Malone posted on Twitter. "You were such an incredible person. You changed so many lives. Had so much love in your heart. You inspired me throughout highschool, and I wouldn't be where I was today without you. Never a more kind and sincere and beautiful person. I f***ing love you mac."
In an interview published weeks before his death, Miller opened up to Rolling Stone about jamming out with the 23-year-old rapper.
"Me and Post have been talking about doing an album," he explained. "So we got together. And then (producer) Frank Dukes has worked on a bunch of my records, but we had never met, so he came through too. And then (musician) Thundercat appeared and we all started jamming."
Malone's tribute comes as editors at TMZ.com reported Miller's final resting place will be a graveyard that was featured in his music video for "Nikes On My Feet". The late rapper's family were seen visiting Homewood Cemetery Friday in his hometown of Pittsburgh, Pennsylvania.
Miller, real name Malcolm McCormick, was found dead at his home in Studio City, California at the age of 26. His cause of death has not yet been revealed.