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Simple Summary: Marek's disease virus is a pathogen capable of inducing tumors, immunosuppression, and paralysis in birds. The degree of virulence is associated with oncogenes such as the meq gene, which is constantly subjected to mutations that can exacerbate clinical manifestations and aid immune escape. This study reports the detection of this virus in backyard and ornamental birds from Brazil and Peru. Through molecular and evolutionary analyses, we determined the circulation of various strains with distinct genetic virulence profiles. Additionally, we identified potential sources of introduction and distribution of this virus among the studied birds, as well as a link between backyard and commercial birds. Given that different bird species exhibit varying degrees of susceptibility or resistance to this virus, the detection and characterization of these strains are crucial for monitoring and preventing potential epidemiological outbreaks in other species. Marek's disease is caused by Mardivirus gallidalpha2, commonly known as Marek's disease virus (MDV). This pathogen infects various bird species resulting in a range of clinical manifestations. The meq gene, which is crucial for oncogenesis, has been extensively studied, but molecular investigations of MDV in noncommercial South American birds are limited. This study detected MDV in backyard and ornamental birds from Brazil and Peru and characterized the meq gene. MDV was confirmed in all seven outbreaks examined. Three isoforms of meq (S-meq, meq, and L-meq) and two to seven proline repeat regions (PRRs) were detected among the sequenced strains. At the amino acid level, genetic profiles with low and high virulence potential were identified. Phylogenetic analysis grouped the sequences into three distinct clusters. Selection pressure analysis revealed 18 and 15 codons under positive and negative selection, respectively. The results demonstrate significant MDV diversity in the studied birds, with both high and low virulence potentials. This study highlights the importance of monitoring and characterizing circulating MDV in backyard and ornamental birds, as they can act as reservoirs for future epidemiological outbreaks. [ABSTRACT FROM AUTHOR]