Background: Lung cancer is the main cause of cancer-related death, with epithelial-mesenchymal transition (EMT) playing an important role in the development of this disease. The EMT-related genes Polypeptide N-Acetylgalactosaminyltransferase 3 (GALNT3) and 2{}^{\prime }-5{}^{\prime }-Oligoadenylate Synthetase 1 (OAS1) are involved in numerous tumor processes. Although these genes have been extensively studied in cancer, they have yet to be analyzed by multi-omics in lung adenocarcinoma (LUAD). Methods: EMT-related genes were identified by R and Venn diagram. Cox regression and Kaplan-Meier analysis were performed to evaluate patient survival, and the Gene Expression Profiling Interactive Analysis (GEPIA) database was used for correlation analysis. GeneCards and R packages were used to explore gene characterization and functional annotation. The Tumor Immune Estimation Resource (TIMER), Human Protein Atlas (HPA), University of Alabama at Birmingham Cancer (UALCAN), and The Cancer Genome Atlas (TCGA) databases were used to investigate gene expression, which was then confirmed by RT-PCR. Clinicopathological analysis was carried out using the UALCAN database. Functional mechanisms and multi-omics analysis were performed using DNA Methylation Interactive Visualization Database (DNMIVD), Targetscan, TIMER, Tumor–immune System Interactions Database (TISIDB) and cBioportal. Diagnostic values were calculated using ROC curve analysis. Results: A total of 320 EMT-related genes were identified in LUAD. Their characteristics were confirmed in the Database for Annotation, Visualization and Integrated Discovery (DAVID) database by the intersection of 855 and 3600 different genes from the Gene Expression Omnibus (GEO) and EMTome databases, respectively. Expression of the EMT-related genes GALNT3 and OAS1 was associated with the prognosis of LUAD patients. A positive correlation was observed between the expression of GALNT3 and OAS1, and their expression was higher in LUAD tissue than in normal lung tissue. This was confirmed using RT-PCR. Multi-omics analysis revealed that GALNT3 and OAS1 expression was associated with gene mutation and methylation, cellular immune infiltration, and several immune subtypes. A miRNA-GALNT3/OAS1 regulatory network was also found. Receiver operating characteristic (ROC) curve analysis found that GALNT3 and OAS1 expression combined had superior diagnostic value to that of each marker alone. Conclusions: GALNT3 and OAS1 expression are associated with immune cell infiltration and poor prognosis in LUAD. Their combined expression has high diagnostic value; hence, GALNT3 and OAS1 may be valuable biomarkers for the early detection of LUAD.