An arrest has been made over the assault of a good Samaritan who stepped in after three Muslim women were abused on a Melbourne train in May.

A 20-year-old Broadmeadows man was nabbed on Friday morning and is expected be charged with assault-related offences.

The attack caused widespread furore after Fairfax Media published a video that captured the tail-end of the vile racial and bigoted attack.

Jasons Cias, 36, the man who came to the defence of the victims, welcomed the arrest on Friday.