Mahatma Gandhi's life can be considered a success in many ways. The most obvious is that the two major goals for which he struggled were both achieved. The first major political goal for which he fought was for equal treatment for "coloureds" (Indians and people of mixed race) in South Africa. South African apartheid, after a prolonged struggle, has ended, and Gandhi very much influenced people like Archbishop Tutu and Nelson Mandela who were architects of its demise.
In India, Gandhi's main objectives were end of British colonial rule and end of sectarian violence. Although Gandhi could be considered successful in ending British rule, partition and ongoing sectarian violence would both be considered failures or disappointments.
From a Platonic point of view, his own philosophy and practice of non-violence would have been successes in acting justly, whatever the outcomes of his actions, because success under the Platonic definition of acting justly is concerned with not committing injustice.