Transient receptor potential (TRP) mucolipins (TRPMLs), encoded by the MCOLN genes, are patho-physiologically relevant endo-lysosomal ion channels crucial for membrane trafficking. Several lines of evidence suggest that TRPMLs mediate localised Ca release but their role in Ca signalling is not clear. Here, we show that activation of endogenous and recombinant TRPMLs with synthetic agonists evoked global Ca signals in human cells. These signals were blocked by a dominant-negative TRPML1 construct and a TRPML antagonist. We further show that, despite a predominant lysosomal localisation, TRPML1 supports both Ca release and Ca entry. Ca release required lysosomal and ER Ca stores suggesting that TRPMLs, like other endo-lysosomal Ca channels, are capable of 'chatter' with ER Ca channels. Our data identify new modalities for TRPML1 action.