Along with Mandera governor-elect Mohamed Khalif, they were welcomed into the fold by Dr Ruto at his Karen residence on Thursday.
"We salute the United Democratic Movement (UDM) leadership for abandoning Azimio La Umoja and joining Kenya Kwanza," said Dr Ruto.
Mr Roba will be joining Dr Ruto's coalition with his UDM party, which he acquired from from the late retired general John Koech to champion North Eastern region issues. Before that, UDM was linked to Dr Ruto but was denied registration in 1999. He left it after failing to wrest control of the outfit from a faction led by the then secretary-general, Mr Martin ole Kamwaro.
UDM has eight MPs, two Senators and two governors.
UDM was founded in 1999 by politicians who were at the time considered renegades of the then ruling party, Kenya African National Union (Kanu). At the time, UDM’s most prominent MP was Hellen Sambili, who served as Minister of East African Cooperation in Kenya's grand coalition government.
Raila, Ruto fight for House
Meanwhile, Azimio and Kenya Kwanza are locked in a battle for the control of Parliament. The former has 159 legislators while the latter has 161.
Of the 12 independent MPs in Parliament, 10 indicated that they will be joining Dr Ruto's Kenya Kwanza.
Among governors, Azimio has 21 elected county bosses while Kenya Kwanza has 22.