Rajagopalchari summed it up pretty well:
'When the independence of India was coming close upon us and Gandhiji was the silent master of our affairs, he had come to the decision that Jawaharlal, who among the Congress leaders was the most familiar with foreign affairs, should be the Prime Minister of India, although he knew Vallabhbhai Patel would be the best administrator among them all. Undoubtedly it would have been better if Nehru had been asked to be the Foreign Minister and Patel made the Prime Minister. I too fell into the error of believing that Jawaharlal was the more enlightened person of the two. A myth had grown about Patel that he would be harsh towards Muslims. This was a wrong notion but it was the prevailing prejudice.'
The simple reason as to why Nehru became PM was that he was, by far, the Congress’ most popular politician, after Gandhi. Right from the 1937 provincial elections, Nehru was the party’s star campaigner, enthralling crowds with his Hindustani oratory. Patel had an iron grip on the Congress party itself but he was many miles behind Nehru as a popular leader. The Sardar himself conceded this: at a massively attended Congress rally in Mumbai, he told American journalist Vincent Sheean, “They come for Jawahar, not for me."
Gandhiji had made his choice known in the favour of Jawaharlal Nehru on 20th April, 1946. This was not the first time that Gandhiji spoke about his choice of Nehru; even before the process of election was set in motion. He had been speaking about it from the last several years.
Maulana Azad expressed his desire for the re-election. This has been accepted by Azad himself, in his autobiography “ ... a general demand arose that I should be selected President for another term…. There was a general feeling in Congress that since I had conducted the negotiations till now, I should be charged with the task of bringing them to a successful close and implementing them.” Maulana’s move agonized his close friend and colleague Jawaharlal who had his own expectations. It upset Gandhiji and on 20.04.1946 he wrote to Maulana Azad, who had already been President of Congress for the last six years: “Please go through the enclosed cuttings.… I have not spoken to anyone of my opinion. When one or two Working Committee members asked me, I said that it would not be right for the same President to continue…. If you are of the same opinion, it may be proper for you to issue a statement about the cuttings [the news item Gandhiji had sent him] and say that you have no intention to become the President again…. In today’s circumstances I would, if asked, prefer Jawaharlal. I have many reasons for this. Why go into them?”
Despite Gandhiji’s open support for Jawaharlal Nehru, 12 out of 15 Pradesh Congress Committees, nominated Sardar Vallabhbhai Patel. No Pradesh Congress Committee proposed the name of Jawaharlal Nehru. J.B Kripalani took the lead in finding the proposers and seconders for Nehru’s candidacy, in deference to Gandhi’s wishes, during the Working Committee meeting on 29.04.1946 in New Delhi. Kripalani succeeded in getting a few Working Committee members and local members of AICC to propose Nehru’s name for the post. However once Nehru was formally proposed by a few Working Committee members, efforts began to persuade Sardar Patel to withdraw his nomination in favour of Jawaharlal. Patel sought Gandhiji’s advice who in turn asked him to do so and “Vallabhbhai did so at once.” Only after Gandhiji was informed that “Jawaharlal will not take the second place” he asked Patel to withdraw. Dr. Rajendra Prasad lamented that Gandhiji “had once again sacrificed his trusted lieutenant for the sake of the ‘glamorous Nehru’.
PCCs who voted for Sardar to elect him as the Congress President, not the Prime Minister of India. Pradesh Congress Committees don’t elect Presidents, delegates of the All India Congress Committee do. Moreover, Nehru was not the Congress President when India gained independence, JB Kripalani was elected Congress President for the crucial years around Indian independence in 1947.
Sardar Vallabhbhai Patel was the most powerful man of his time. The Mahatma was the most respected, Jawaharlal Nehru the most loved and Subhas Bose the most longed-for. But in terms of the iron control he exercised over the largest political apparatus in the country and the grip he had on political currents and cross-currents in virtually every province in India, the power wielded by Patel had no match. Gandhi loved Jawaharlal, trusted Prasad, admired Rajaji, esteemed Azad. But Patel, he leaned on and laughed with. Patel regarded Gandhi as his mentor, his leader.
Nehru and Patel were in fact not rivals but comrades and co-workers. They worked closely together in the Congress from the 1920s to 1947; and even more closely together thereafter, as prime minister and deputy prime minister in the first government of free India. Independence and Partition, Nehru and Patel worked shoulder-to-shoulder in building a united and democratic nation. Nehru and Patel shared a deep love of their country, an abiding commitment to its unity, and, not least, a sense that they owed it to the memory of their common Master, Mahatma Gandhi, to work together, and to work ferociously hard too. AS Iyengar remarked: “Both are untiring workers, allowing themselves practically no rest, either physical or mental.” Patel represented Indian nationalism's Hindu face, Nehru India's secular and also global face. Their partnership, necessary and fruitful for the country, was a solemn commitment that each made to the other.
Last but not the least, we must not forget why Gandhi had chosen Jawaharlal over Patel: appeal among all communities and groups, international stature, moderation, age, health etc. Patel himself wrote in 1949 that it was fitting that Nehru came to head the country after Independence:
'The sincerity of his convictions, the breadth of his outlook, the clarity of his vision, and the purity of his emotions – all these have brought to him the homage of millions in this country and outside.It was, therefore, in the fitness of things that in the twilight preceding the dawn of independence he should have been our leading light, and that when India was faced with crisis after crisis, following the achievement of our freedom, he should have been the upholder of our faith and the leader of our legions. No one knows better than myself how much he has labored for his country in the last years of our difficult existence. I have seen him age quickly during that period, on account of the worries of the high office that he holds and the tremendous responsibilities that he wields'.
In 1951, First General Elections were held in India, Indian National Congress won the election, winning 364 out of 489 seats, i.e.75%. Hence being the ruling party it was totally an internal matter for the Congress for so as to whom to choose the Prime Minister. Nehru being on height of his popularity, it was a unanimous vote in the Congress to make him the Prime Minister.
Choosing the First Prime Minister of India
Only Nehru-Gandhi baiters, especially with RSS inclinations, argue that Patel would have made better PM than Nehru for independent India. The Nehru baiters have known very less about Nehru & Patel and nothing about Gandhi while doing so. The truth remains that Nehru was the most popular Congress leader among the people of India, next only to Gandhi, during 1930's & 40's, the fact which was conceeded by Patel himself. PCC's can only file nominations for Congress President position to be elected by AICC delegates but not the position of Prime Minister. Nehru's goodwill with Mountbatten's had its effect on smooth transition of power at the time of independence. Despite certain short comings, Nehru could lay solid foundation for building institutions for modern India, project its secular & non-aligned approach in the bi-polar world etc. Subsequently corruption, social degradation etc pulling down India's progress can't be blamed on Nehru.