The high centre-of-mass energy $(\sqrt{s})$ of proton-proton collisions and the large available datasets at the CERN Large Hadron Collider allow the study of rare processes of the Standard Model (SM) with unprecedented precision. Precise measurements of such rare processes provide stringent tests of SM, with the potential to unveil discrepancies between data and SM predictions or provide important input for the improvement of theoretical calculations. In this contribution, measurements of top-quark production in association with a photon, $Z$ or $W$ boson in data recorded with the ATLAS experiment at $\sqrt{s}=13$ TeV are presented. These measurements provide important bounds on the electroweak couplings of the top-quark and constrain backgrounds that are important in searches for Higgs production and for new phenomena beyond the SM.