In this paper we investigate critical Gagliardo-Nirenberg, Trudingertype and Brezis-Gallouet-Wainger inequalities associated with the positive Rockland operators on graded groups, which includes the cases of R n , Heisenberg, and general stratified Lie groups. As an application, using the critical Gagliardo-Nirenberg inequality the existence of least energy solutions of nonlinear Schrödinger type equations is obtained. We also express the best constant in the critical Gagliardo-Nirenberg and Trudinger inequalities in the variational form as well as in terms of the ground state solutions of the corresponding nonlinear subelliptic equations. The obtained results are already new in the setting of general stratified groups (homogeneous Carnot groups). Among new technical methods, we also extend Folland's analysis of Hölder spaces from stratified groups to general homogeneous groups.2010 Mathematics Subject Classification. 35J35, 35G20, 22E30, 43A80.