 Nyorai kupfuurira kweiyi ndima - Muna 1787, Morris akasarudzwa senhume kuPhiladelphia Convention, rakanyora ndokuronga bumbiro idzva reUnited States. Morris aisataura kakawanda pakokorodzano yacho, asi bumbiro remitemo rakabudiswa pakokorodzano yacho rakaratidza pfungwa dzake dzakawanda. Morris nevamwe vake vakabatsira kuti Pennsylvania ibvumire bumbiro idzva, uye gwaro racho rakabvumirwa nenhamba yaidiwa yenyika pakupera kwa1788. Paramende yePennsylvania yakabva yasarudza Morris semumwe wevamiriri vayo vaviri vekutanga muUnited States Senate. Morris akaramba kupiwa naWashington kuti ashande soMunyori weHurumende wokutanga wenyika, panzvimbo pezvo achikurudzira Alexander Hamilton nokuda kwechinzvimbo chacho. MuSeneti, Morris akatsigira chirongwa chezvoupfumi chaHamilton ndokubatana neFederalist Party. Mukati uye pashure pokushumira kwake muSeneti, Morris akapinda zvikuru muzvikwereti achifungidzira pamusoro penyika inotungamirira kuKutya kwe1796-97. Asingakwanisi kubhadhara vakweretesi vake, akaiswa mufurati revakweretesi rePrune Street riri pedyo neWalnut Street Prison kubva muna 1798 kusvika muna 1801. Pashure pokusunungurwa mutorongo, akararama upenyu hwakanyarara, hwokuzvimirira mumusha wakaderera muPhiladelphia kutozosvikira parufu rwake muna 1806. 