The chemical reactions and pathways resulting in the formation of trypanothione (N1,N6,-bis(glutathionyl)spermidine) in two steps from glutathione and spermidine via an N1- or N8-glutathionylspermidine intermediate. Trypanothione appears to be an essential redox intermediate in intracellular thiol redox regulation. It also plays a role in protecting against oxidative stress. [ https://biocyc.org/META/NEW-IMAGE?type=NIL&object=TRYPANOSYN-PWY http://www.ncbi.nlm.nih.gov/pubmed/9677355 ]