He held that variation was predetermined by a higher intelligence, and that evolution proceeded in a step-wise fashion, and not an accumulation of small variations.
In Jan 1871 he published Genesis of Species, opposing Darwin's interpretation of evolution. Mivart's liberal position even seemed to conflict with his Roman Catholic religion, for which he was excommunicated by Cardinal Vaughan in Jan 1900, a few months before he died. link
In a letter (1871) to Darwin after the publication of Mivart's Genesis of the Species, he states,
"Unhappily the acceptance of your views means with many the abandonment of belief in God and in the immortality of the soul together with future rewards & punishments. No words of mine could represent an appreciable fraction of what I think as to the importance of such an abandonment—yet I am far from blaming you personally for (knowing you as I do) I am persuaded you only seek the promotion of truth though I regret you do not more protect against these unnecessary irreligious deductions."