The 25-year-old is now sponsored by the sports apparel brand along with the likes of Ronda Rousey, Conor McGregor, Anthony Pettis and Johny Hendricks.
The announcement comes on the eve of the UFC Fight Kit unveiling in late June.
"They have good designers, good taste and they'll be able to listen to me and take my likes into consideration," MacDonald told MMAjunkie.
"Reebok is an amazing company. It's great for my brand, great for Reebok. It's going to be a great relationship for years to come," he added.
If he beats Lawler on Saturday night MacDonald will pocket $30,000.