Background Robotic surgery has been widely adopted for complex procedures to overcome technical limitations of open or laparoscopic methods. However, evidence of any subsequent benefit is lacking. This study was undertaken to compare open, laparoscopic, and robotic gastrectomy in technically demanding procedure—D2 dissection in obese patients with gastric cancer. Methods Data collected between 2010 and 2018 on D2 gastrectomy in obese patients with gastric cancer were used to conduct retrospective analysis, comparing short- and long-term outcomes of open, laparoscopic, and robotic techniques. Results In a total of 185 patients, there were 69 open, 62 laparoscopic, and 54 robotic gastrectomy procedures. Median ages for respective surgical groups were 66 (interquartile range IQR: 61–64 years), 63 (IQR: 59–63), and 59 years (IQR: 56–60 years) ( p  = 0.009). Early-stage gastric cancer ranked proportionately higher in the laparoscopic group ( p  = 0.005), but operative times were similar among groups. Estimated blood loss ( p  < 0.001) and drainage volumes ( p  = 0.001) were higher in the open group, relative to others. Although a robotic approach performed best in overall compliance and in mean number of retrieved lymph node, observed rates of early or late complications did not differ by technique. The open group experienced significantly poorer overall ( p  = 0.039) and relapse-free ( p  < 0.001) survival compared with the laparoscopic or robotic group. Robotic surgery emerged from multivariable Cox regression as a protective factor for relapse-free survival (HR = 0.314, 95% CI 0.116–0.851). Conclusions In obese patients with gastric cancer, robotic gastrectomy with D2 lymphadenectomy proved comparable to open or laparoscopic technique short-term, yielding better long-term outcomes.