The long-term timing of radio pulsars yields a rich vein of science. The Thousand Pulsar Array (TPA) programme uses the power of MeerKAT in sub-array mode to monitor and time more than 500 pulsars with a monthly cadence. This allows us to explore the turbulent, magnetic structure of the interstellar medium through the time-variability of the dispersion and rotation measures. More importantly it sheds light on the spin-down history of these pulsars and the correlation between changes in the torque and observed radio profile shapes. Understanding this behaviour is a critical component in the detection of gravitational waves through pulsar timing arrays. In this talk I will introduce the TPA long-term monitoring programme, provide an overview of the current project status and describe key science results, including measurements of pulsar viewing and magnetic geometries, assessing the stability of pulsar spin-down rates with time, and an observationally driven unification of the bulk properties of young and millisecond pulsars.