The preparation of basalt and S‐glass fiber‐reinforced poly(dicyclopentadiene) via ring‐opening metathesis polymerization using a thermally latent pre‐catalyst, that is, Mo(N‐3,5‐Me2‐C6H3)(= CH‐(2‐MeO‐C6H4))(IMes)(OTf)2 (1, IMes = 1,3‐dimesitylimidazol‐2‐ylidene; OTf = SO3CF3) is reported. Complementarily, the non‐latent first‐generation Grubbs initiator RuCl2(PPh3)2(CHPh) (2) is used. 2 can be rendered latent by the addition of ppm amounts of triphenylphosphine (PPh3). Both 1 and 2/PPh3 allow the realization of thermally latent single‐component systems with sufficient pot life that do not require pre‐mixing of the individual components shortly before use. The prepared fiber matrix composites are characterized in terms of mechanical, thermal, and chemical stability.