After briefly considering Lev Mey's The Tsar's Bride as a subject (later taken up in 1898 by Nikolay Rimsky-Korsakov, his 9th opera), Borodin began looking for a new project for his first opera. Vladimir Stasov, critic and advisor to The Mighty Handful, suggested The Lay of Igor's Host, a 12th-century epic prose poem, and sent Borodin a scenario for a 3 Act opera on 30 April 1869. Initially, Borodin found the proposition intriguing, but daunting:
"Your outline is so complete that everything seems clear to me and suits me perfectly. But will I manage to carry out my own task to the end? Bah! As they say here, 'He who is afraid of the wolf doesn't go into the woods!' So I shall give it a try..."—Aleksandr Borodin, reply to Stasov's proposal
After collecting material from literary sources, Borodin began composition in September 1869 with initial versions of Yaroslavna's arioso and Konchakovna's cavatina, and sketched the Polovtsian Dances and March of the Polovtsy. He soon began to have doubts and ceased composing. He expressed his misgivings in a letter to his wife: "There is too little drama here, and no movement... To me, opera without drama, in the strict sense, is unnatural." This began a period of about four years in which he proceeded no further on Prince Igor, but began diverting materials for the opera into his other works, theSymphony No 2 in B minor (1869–76) and the collaborative opera-ballet Mlada (1872).
The Mlada project was soon aborted, and Borodin, like the other members of The Mighty Handful who were involved—César Cui, Modest Mussorgsky, and Rimsky-Korsakov—thought about ways to recycle the music he contributed. Of the eight numbers he had composed for Act 4 of Mlada, those that eventually found their way into (or back into) Prince Igor included No.1 (Prologue: The opening C major chorus), No.2 (material for Yaroslavna's arioso and Igor's aria), No.3 (Prologue: The eclipse), No.4 (Act 3: The trio), and No.8 (Act 4: The closing chorus).
Borodin returned to Prince Igor in 1874, inspired by the success of his colleagues Rimsky-Korsakov and Mussorgsky in the staging of their historical operas, The Maid of Pskov (1873) and Boris Godunov(1874). This period also marks the creation of two new characters, the deserters Skula and Yeroshka, who have much in common with the rogue monks Varlaam and Misail in Boris Godunov.
In his memoirs, Rimsky-Korsakov mentions an 1876 concert at which Borodin's "closing chorus" was performed, the first public performance of any music from Prince Igor identified by him:
"...Borodin's closing chorus ["Glory to the beautiful Sun"]..., which, in the epilogue of the opera (subsequently done away with) extolled Igor's exploits, was shifted by the author himself to the prologue of the opera, of which it now forms a part. At present this chorus extolls Igor as he starts on his expedition against the Cumans/Polovtsy. The episodes of the solar eclipse, of the parting from Yaroslavna, etc., divide it into halves which fringe the entire prologue. In those days this whole middle part was non-existent, and the chorus formed one unbroken number of rather considerable dimensions." —Nikolay Rimsky-Korsakov, Chronicle of My Musical Life, 1909
The idea of a choral epilogue in the original scenario was no doubt inspired by the example of A Life for the Tsar by Glinka, to whose memory Prince Igor is dedicated.
Borodin's primary occupation was chemistry, including research and teaching. However, he also spent much time in support of women's causes, much to the consternation of his fellow composers, who felt he should devote his time and talent to music. In 1876, a frustrated Stasov gave up hope that Borodin would ever finish Prince Igor, and offered his scenario to Rimsky-Korsakov. Rimsky-Korsakov instead assisted Borodin in orchestrating important numbers in preparation for concert performance—for example, the Polovtsian Dances in 1879:
"There was no end of waiting for the orchestration of the Polovtsian Dances, and yet they had been announced and rehearsed by me with the chorus. It was high time to copy out the parts. In despair I heaped reproaches on Borodin. He, too, was none too happy. At last, giving up all hope, I offered to help him with the orchestration. Thereupon he came to my house in the evening, bringing with him the hardly touched score of the Polovtsian Dances; and the three of us—he, Anatoly Lyadov, and I—took it apart and began to score it in hot haste. To gain time, we wrote in pencil and not in ink. Thus we sat at work until late at night. The finished sheets of the score Borodin covered with liquid gelatine, to keep our pencil marks intact; and in order to have the sheets dry the sooner, he hung them out like washing on lines in my study. Thus the number was ready and passed on to the copyist. The orchestration of the closing chorus I did almost single-handed..." —Nikolay Rimsky-Korsakov, Chronicle of My Musical Life, 1909
Borodin worked on Prince Igor, off and on, for almost 18 years.