Ioane, 24, played five games for the Dragons after joining them mid-season from the Gold Coast Titans.
London coach Andrew Henderson was pleased with the signing of Ioane, who despite a glittering junior resume, never really delivered on his promise at NRL level.
“I’m very pleased that we have been able to bring Mark to the club for the next two seasons. It is very rare that a Championship club can attract a player with Mark’s NRL experience and his excellent rugby league pedigree.
“Mark has come through the New Zealand Warriors’ youth system and has gone on to average over 10 NRL appearances per season over the past three years which is a very good achievement considering that he is still young as a prop.”