YS Chowdary, C M Ramesh, Garikapati Mohan Rao and T G Venkatesh met Rajya Sabha Chairman M Venkaiah Naidu and handed him a letter of a resolution passed by the legislature party urging its merger.
In their letter to Venkaiah Naidu, the TDP MPs wrote that they were "inspired and encouraged by the impeccable leadership of Narendra Modi" and were hence merging with the BJP.
Addressing a press conference BJP Rajya Sabha MP Bhupender Yadav said: "Four TDP Rajya Sabha members held a meeting earlier in the day where they decided to merge with the BJP."
After the four MPS joined the BJP, party working president J.P. Nadda said the MPs were thinking for long to follow the dynamic leadership of Prime Minister Narendra Modi and for the development of Andhra Pradesh.
Taking stock of the situation, Naidu, who is vacationing in Europe, spoke to a couple of senior party leaders here over phone, party sources said.
Naidu enquired about the rebellion and told the leaders that such crises were not new to TDP, they said.
TDP fought with the BJP only for securing the state's interests, the sources quoted him as having said.
BJP's working president J P Nadda and leader of the BJP in Rajya Sabha Thawarchand Gehlot also met Naidu and submitted a proposal from BJP president Amit Shah saying the party has no objection to the merger of the TDP Legislature party with the BJP.
Three of the four MPs later met Nadda and Gehlot at the party headquarters and joined the BJP.
"I assure them that the BJP believes in politics of positivity and inclusiveness," Nadda told a press conference in the presence of TDP MPs.
Their decision to back the BJP will give a boost to the saffron party in the upper house as the ruling National Democratic Alliance does not have a majority there yet.
The TDP, which is led by former Andhra Pradesh chief minister N Chandrababu Naidu, also has three MPs in the Lok Sabha.
The Rajya Sabha has a strength of 245 members and the BJP is the single largest party with 71 MPs.