With Modi yet to announce the makeup of this cabinet, the ceremony at the presidential palace on Sunday evening (13:45 GMT) will be keenly watched when some 30 ministers-to-be also take the oath on the constitution.
Modi's Hindu-nationalist Bharatiya Janata Party (BJP) ruled outright for the past decade but failed to repeat its previous two landslide wins this time around, defying analysts' expectations and exit polls.
He was instead forced into quick-fire talks with the 15-member coalition, the National Democratic Alliance (NDA), which guaranteed him the parliamentary numbers to govern, reports BSS.
Larger coalition parties have demanded hefty concessions in exchange for their support.
The Hindustan Times described days of "hectic talks", while the Times of India said the BJP had sought to "pare down" their partners' demands.
It is widely reported that the Telgu Desam Party (TDP), the largest BJP allywith 16 seats, has extracted four cabinet positions.
The next biggest party, the Janata Dal (United) with 12 seats, has negotiatedtwo.
Modi's previous cabinet had 81 ministers.
- Off-limits' -
But Indian media reported widely that the top jobs including the four mostpowerful posts of the interior, foreign, finance and defence would remain inthe BJP's grip.
"Key ministries like home, defence, finance, and external affairs are off-limits," the Times of India reported.
It suggests that top Modi aides Amit Shah, Rajnath Singh and Nitin Gadkari --interior, defence minister and transport ministers respectively -- will be inthe new team.
Analysts said that the coalition will shift parliamentary politics and force Modi's once domineering BJP into a some what more conciliatory approach.
"In the past, the BJP has had confidence because of its sheer majority," said Sajjan Kumar, head of the Delhi-based political research group PRACCIS.
"The coalition will now force the BJP to engage in more consultation."
Zoya Hasan of Jawaharlal Nehru University said Modi faced potentialchallenges ahead -- warning he may be "meeting his match" in the "craftypoliticians" of the TDP's Chandrababu Naidu and JD(U)'s Nitish Kumar.
- Opposition nominate Rahul Gandhi -
Security was tight in the capital New Delhi on Sunday, with thousands oftroops and police deployed as regional leaders flew in.
Bangladeshi Prime Minister Sheikh Hasina and Sri Lankan President RanilWickremesinghe -- as well as leaders including those of Bhutan, Nepal and theMaldives -- are to due to attend the ceremony and following state banquet.
Neighbouring rivals China and Pakistan are notably absent in not sending atop leader.
Modi on Sunday laid flowers at the memorial to father of the nation MahatmaGandhi, before the Hindu nationalist leader paid his respects at the nationalwar memorial.
Modi's chief rival, Rahul Gandhi, was nominated on Saturday to lead India'sopposition in parliament, after he defied analysts' forecasts to help theCongress party nearly double its parliamentary numbers.
It was Congress's best result since Modi was swept to power a decade ago,rescuing the party from the political wilderness.
A meeting of the Congress leadership on Saturday voted unanimously torecommend Gandhi's election as India's official opposition leader, a postthat had been left vacant since 2014.
Gandhi is the scion of the dynasty that dominated Indian politics for decadesand is the son, grandson and great-grandson of former prime ministers,beginning with independence leader Jawaharlal Nehru.
If elected, as expected, he will be recognised as India's official oppositionleader when the new parliament sits, which local media reports suggest willhappen as soon as early next week.
Parliamentary regulations require the opposition leader to come from a partythat commands at least 10 percent of the lawmakers in the 543-seat lowerhouse.
The post has been vacant for 10 years because two dismal election results forCongress -- once India's dominant party -- left it short of that threshold.