The controversial politician had to step down as minister eight months ago over the killing of a deputy superintendent of police.
He was sworn in as a minister again in the presence of the ruling Samajwadi Party chief Mulayam Singh Yadav on Friday.
Raja Bhaiya said the cases against him were all based on trumped up charges "engineered" by former chief minister Mayawati.
The Central Bureau of Investigation (CBI) earlier gave a clean chit to Raghuraj Pratap Singh alias Raja Bhaiya in connection with the killing of Deputy Superintendent of Police (DSP) Zia-ul-Haque.
In June, Raja Bhaiya underwent a polygraph test at Central Forensic Science Laboratory (CFSL) in New Delhi.
"I want the truth to come out....I am ready to undergo a lie detector test," Raja Bhaiya had told media.
Haque's wife had earlier accused that Raja Bhaiya was involved in her husband's murder.
Zia-ul-Haque was killed, along with Kunda village head Nanhe Yadav, over a land dispute and in the violence that followed at Pratapgarh district in Uttar Pradesh in March.
The Samajwadi Party (SP) strongman and four others were named in one of CBI's four FIRs in connection to the murders.
Raja Bhaiya had resigned after he was booked in the killing of the DSP.
--IBNS (Posted on 11-10-2013)