Ram Kumar Kashyap, sitting INLD MP in Rajya Sabha, joined the BJP on Wednesday in the presence of party working president JP Nadda.
Kashyap was the lone Indian National Lok Dal (INLD) MP in the upper house of the Parliament.
With this, the BJP's strength in the Rajya Sabha has increased to 76.
Besides Kashyap, two-time former MP from Kannur in Kerala AP Abdullakutty, who has been in the CPI(M) and the Congress, also joined the BJP on Wednesday.
He was expelled from the CPI(M) in 2009 for praising the then Gujarat Chief Minister Narendra Modi.
He then joined the Congress, which recently sacked him for praising Narendra Modi yet again.
On Tuesday, two INLD MLAs Zakir Hussain and Parminder Singh Dhul had also joined the BJP.