His fairly brief English Wikipedia entry is here, and more information about him can be found in his French Wikipedia entry here.
As best I can tell from these and a few other Internet sources, Doré had little or no formal art training, though he was the friend of artists who might have given him tips now and then.
The images of his paintings below are arranged chronologically.
Ninth Circle of Hell, an impressive painting similar to his illustration work.
Again illustration-like, but not as good as the previous painting.
Being a skilled draftsman, that carried over into this oil painting.
Doré might have lacked academic training, but he painted scenes that academicians would have.
Doré was trapped in Paris during the Franco-Prussian War siege and was a member of la garde nationale during the time of the Commune.
He had business interests in Britain and traveled there, hence this and other landscape paintings.
Another religious painting.
Perhaps Doré's last painting.