Lowassa defected in late July after he was eliminated from the list of presidential aspirants for the ruling party Chama Cha Mapinduzi (CCM). He announced his intention to run for the opposition bloc Chama Cha Demokrasia and Maendeleo (Chadema) shortly after.
Lowassa claims that he unfairly lost his bid to become the ruling party's candidate. He now represents a union of four political parties fighting for the adoption of a new constitution.
Given that Lowassa commands huge support, especially from young people, this is the first time during the history of multiparty politics that the country's opposition has a genuine chance of winning.
After Lowassa’s defection, a number of key members of the ruling party including Members of Parliament, councilors and regional officials followed him to Chadema.
His switchover has ruffled feathers, however.
Until recently, Chadema considered Lowassa corrupt and unprincipled. Chadema led calls for him to go when he was implicated in a corruption scandal that culminated in his resignation in 2009.
He has constantly denied that his office was involved in accepting kickbacks for a major energy contract from American company Richmond Development.
Some members of Chadema have left the party in protest.
But Chadema's chances may be boosted by the appearance of Juma Duni Haji as Lowassa's running mate.
Haji, who has run on opposition tickets in Tanzanian presidential elections in the past, was Minister of Infrastructure and Communications until Lowassa defected.