Oligomerisation of transcription factors controls their translocation into the nucleus and DNA binding activity. Here we present a fluorescence microscopy method termed pCOMB (pair correlation of molecular brightness) that tracks the mobility of different oligomeric species within live cell nuclear architecture1. pCOMB amplifies the signal from the brightest species present and filters the dynamics of the extracted oligomeric population based on arrival time between two locations. Here we use this method to demonstrate a dependence of signal transducer and activator of transcription 3 (STAT3) mobility on oligomeric state. We find that upon entering the nucleus STAT3 dimers must first bind DNA to form STAT3 tetramers, which are also DNA-bound but exhibit a different mobility signature. Examining the dimer-to-tetramer transition by a cross pair correlation analysis (cpCOMB) reveals chromatin accessibility to modulate STAT3 tetramer formation. Thus the pCOMB approach is suitable for mapping the impact oligomerisation has on transcription factor dynamics.