This study characterised how the Ku protein from Mycobacterium tuberculosis drives DNA repair, solving cryo-EM structures of apo and DNA-bound Ku and showing that Ku forms extended filaments that promote DNA synapsis. As one of several complementary biophysical methods, Flow Induced Dispersion Analysis (FIDA), run on the Fida 1 system, was used to measure the hydrodynamic radius of fluorescently (FAM) labelled DNA as Ku concentrations increased. The FIDA data captured a decrease then a pronounced increase in hydrodynamic radius, supporting an initial high-affinity Ku-DNA binding event followed by lower-affinity oligomerisation of Ku:DNA complexes in solution. FIDA complemented mass photometry, cryo-EM and atomic force microscopy.