Sensor node localization is a challenging task because of severe constraints on cost, energy, and effective range of sensor devices. To overcome limitations in existing solutions, this paper formally describes, designs, implements, and evaluates a Convex Optimization-based Method for Event-Driven Localization, i.e., COMEDL, in large-scale wireless sensor networks. The key idea behind COMEDL is to estimate the two-dimensional location coordinates of sensor nodes by processing multiple one-dimensional node sequences that can be easily obtained via loosely guided localization event distributions. The proposed design is evaluated through theoretical analysis, extensive simulations, and physical experiments (an indoor test-bed with 44 MICAz sensor nodes). Evaluation results demonstrate that COMEDL can effectively localize nodes with improved accuracy and flexibility.