Ultra-cool dwarfs (UCDs) are the lowest-mass, coldest, and faintest products of star formation. With spectral types later than M7, effective temperatures below 2600 K, and luminosities less than 1/1000 that of the Sun, they are compelling as well as challenging targets in astronomy. Despite their abundance, UCDs remain an observationally elusive population, due to their intrinsically low luminosity, making them hard targets for Gaia and ground-based telescopes. However, Euclid’s wide and deep near-infrared surveys promise to revolutionise the field, enabling the detection of an unprecedented number of new sources. 

Using Euclid Quick Release 1 data, we investigate a large sample of UCDs. I explore the spectral features of UCD candidates selected as contaminants in the QSO search in Euclid Deep Field North and confirm their UCD identity. By identifying known UCDs within the Euclid dataset, I refine the spectroscopic selection criteria for UCDs. Spectroscopic data from Q1 allow for a detailed examination of stellar parameters, photometric distances, and other details of individual UCDs, including features in water absorption regions. Additionally, fluxes appropriate for point-like objects are filtered from Euclid MER photometry, and the UCDs are characterised in various colour-colour diagrams, in an effort to distinguish them from QSOs, their major contaminants. 

Combined spectroscopic features and photometric analysis reveal intriguing candidates, many of which exhibit high proper motions, consistent with nearby low-mass objects. We also explore the synergy between Euclid and Gaia observations for UCDs, resulting in a robust combined spectral analysis of the targets, including the derivation of stellar radius. Two of the new candidates have been followed up with ground-based spectroscopic observations, independently validating Euclid detections. 

As the Euclid mission progresses, the resulting UCD dataset will expand significantly, promising to improve our understanding of very low-mass stars, refining the substellar mass and luminosity functions, and offering new insights into the history of substellar formation and the chemical evolution of the Galaxy.