He was not "not treated fairly" by the party, a source close to Singh claimed.
Senior BJP leader and former Madhya Pradesh minister Rustam Singh resigned from the party on Monday, ahead of the state assembly polls scheduled next month.
In a letter addressed to state BJP president Vishnu Dutt Sharma, Singh (78) said he is resigning from the BJP's primary membership and all party positions.
He was not "not treated fairly" by the party, a source close to Singh claimed.
Rustam Singh's son Rakesh Singh has been fielded by the Bahujan Samaj Party from Morena seat. Since then, there was speculation that Rustam Singh may leave the ruling BJP to campaign for his son in Morena.
An influential Gurjar leader from the Gwalior-Chambal region, Rustam Singh resigned from the Indian Police Service (IPS) in 2003 and joined the BJP.
He was an MLA for two terms, from 2003-2008 and 2013-2018.
Rustam Singh served as a minister for two terms from 2003-2008 and 2015-2018.
Elections to the 230-member state assembly are scheduled on November 17.
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