Plants have a variety of enzymes which help defend from pathogen attack by producing antimicrobial compounds. One of these enzymes, agmatine coumaroyl transferase (ACT) is responsible for producing hydroxycinnamic acid amides (HCAAs). In this study, we identified a tightly clustered group of ACT genes in Brachypodium distachyon responsive to Fusarium infection and functionally characterised one of these genes designated as BdACT2a. It was found that when expression of BdACT2a is disrupted, Brachypodium becomes more susceptible to Fusarium pseudograminearum. BdACT2a has broad substrate specificity and feruloylagmatine is produced in significantly lower quantities in the Bdact2a line compared to wild-type Brachypodium. Feruloylagmatine appears to inhibit spore germination but not mycelium growth of Fusarium. This report demonstrates that BdACT2a is important for plant defence and ACTs may have a conserved defensive role in plants.