While resistance spot welding (RSW) have been the most successful sheet metal joining process in automotive industry, there are certain limitations due to the access of welding guns and electrodes. A large C-type gun has to be employed for body floor assembly. Laser or arc welding is used to weld a closed section and hydroformed parts where RSW is hard to apply. In this research, an automated single-sided spot welding system is introduced to overcome typical RSW issues and its applications to automotive body assembly are presented. This new welding machine is designed to make a weld by single-side access with low electrode force. Weldability lobe curves were developed to find applicable operating conditions and found that relatively low welding current was possible to make a reasonable size of weld nugget. Various applications for body-in-white were investigated. Hydroformed side member parts and brackets were welded together and got successful results. Large floor panels were joined together with a small-sized single-sided welding gun. Thanks to the low electrode force of the machine, good appearance can be achieved as an indentation-free weld for the outer panel. Although a few limitations and challenges have to be considered to maintain a good-quality weld, this technique can be a great alternative to hard-to-spot weld applications on automotive body assembly. The weldability lobe curve shows that operating points can be found at a relatively low welding current range due to the low electrode force. Because only one-side access is necessary to make a good weld, great potential advantages can be found in joining of large panels. Hard-to-spot weld applications, such as hydroformed or closed-section parts, were also possible to make a resistance spot weld. Due to the simple system configuration and easy-access capability, productivity can be increased by improving cycle time and reducing maintenance efforts. Although some limitations exist, this technique can be a great alternative to conventional single-sided sheet metal joining processes.