Plant pathogens are responsible for many crop plant diseases, resulting in economic losses. The use of bacterial agents is an excellent option to fight against plant pathogens and an excellent alternative to the use of chemicals, which are offensive to the environment and to human health. Two of the most common biocontrol agents are members of the Bacillus and Pseudomonas genera. Both bacterial genera have important traits such as plant growth-promoting (PGP) properties. This review analyzes pioneering and recent works and the mechanisms used by Bacillus and Pseudomonas in their behavior as biocontrol and plant growth-promoting agents, discussing their mode of action by comparing the two genera. Undoubtedly, future integrated research strategies for biocontrol and PGP will require the help of known and novel species of both genera.