1856 is considered to be the year of the foundation of the Tretyakov Gallery. It was then, when Pavel Tretyakov bought first two pictures of Russian artists: N.Shildera's "Temptation" and V.Khudyakov’s «Skirmish with the Finnish smugglers». At the end of 1850-s he acquired several more canvases: I.Sokolov’s «Gathering of cherries», V.Jakobi’s "Messenger", pictures of A.Savrasov, M.Klodt etc. Possibly, at that very time Tretyakov got the idea to create a museum of national Russian painting.

Pavel M.Tretyakov, 1871

In 1860 he went on his first foreign business trip. Before leaving, he made his last will. He stated: "I bequeath the sum of 150,000 silver rubles for the foundation of an art museum or a public picture gallery in Moscow […]". Driven by this idea, he continued picking up paintings. Actually, he had no experience in collecting artworks and could rely only on his own taste. In 1860th pictures «Halt of prisoners» by V.Jakobi, «Last spring» by M.Klodt, «Grandmother's dreams» by V.Maksimov and others appeared in the collection.

Sincere friendship joined Tretyakov with many artists. In some cases he supported them financially, in other cases the acquisition of an artist’s painting would determined his subsequent career.
Vasily Perov's picture «Rural icon-bearing procession on Easter» (1861) was that very case. Though people disapproved of the anticlerical message of the canvas and the Holy Synod considered it to be “an immoral painting”, Tretyakov highly appreciated Vasily Perov's work.
Later on he would acquire Perov’s "Troika" and "Dilettante". Tretyakov not only bought Perov's pictures, he also ordered him portraits, and when the artist passed away he took active part in the organization of his posthumous exhibition.

In the second half of the 19th century realistic manner of painting was a way to criticize the drawbacks of society and social life. Thus "Unequal Marriage" by V.Pukirev (1862), "Alumna" by N.Nevrev (1867), "Knjazhna Tarakanova" by K.Flavitsky (the first picture on Russian history bought for the Gallery) appeared in the collection. These pictures were devoted to a pressing issue of the day – women, deprived of civil rights. Tretyakov’s true concern of women’s rights was demonstrated by another statement in his last will: "[…] I bequeath 8, 186 rubles plus later percents of this sum for poor brides could marrying decent men".

Tretyakov was fond of nature and felt it very well. That’s why the acquisition of landscapes of L.Lagorio, A.Bogoljubov, M.Klodt and I.Shishkin was not done just by chance. Tretyakov wrote to one of the artists: «I don’t need rich nature or a magnificent composition, the bright light or miracles. Let it be a dirty pool, but let it be real and poetic. There is poetry everywhere – and that is a task of an artist to see and show it».

I.N.Kramskoy, 1876

Portraits were of special interest to Tretyakov. In 1860-s in Italy he acquired a portrait of the Italian archeologist of M.Lanchi by Karl Brullov, followed by portraits of architects A.Gornostaev and I.Monigetti, poet V.Zhukovsky and others, also by Bryullov. Later a portrait of V.Zubova by V.Tropinin was bought. By the end of 1860-s Tretyakov conceived the idea of creating a portrait series of his contemporaries - outstanding Russian composers, writers, artists.
Not only he used to buy finished pictures, but also ordered portraits to the artists. Thus according to Tretyakov’s request Vasily Perov made portraits of A.Ostrovsky, F.Dostoevsky, A.Maykov, M.Pogodin, V.Dahl and I.Turgenev; and Ivan Kramskoy created portraits of L.Tolstoy, M.Saltykov-Shchedrin, S.Aksakov and N.Nekrasov.

It was not at all easy to get some portraits. A story of creating Leo Tolstoy's portrait (1873) by I.Kramskoy was quite interesting. For a long time Tretyakov had been dreaming of a portrait of Leo Tolstoy, but the great writer was "strongly against the idea". During four years many people tried to convince him, but all the attempts were useless.Then Kramskoy put forward a weighty argument: "[…] I will not paint your portrait, and none of my contemporaries will, but in some 30, 40, 50 years someone will certainly do, and then we all will regret that it wasn't done in time". Leo Tolstoy accepted the argument, but asked the artist to paint two portraits, one for Tretyakov's collection and the other for him. Kramskoy agreed and two portraits were created.

Another story is about Nicolay Nekrasov’s portrait. The poet was very ill and stayed in bed when Kramskoy began drawing his portrait. Nekrasov died in December 1877, and Kramskoy finished his work by memory. As a result the picture consisted of several parts: the head of the poet was painted on a small separate canvas when Nekrasov was still alive and could sit for his portrait. Kramskoy glued this part onto the canvas of his painting "Nekrasov in the Period of his Last Songs" (1878).

I.E.Repin, 1900

Tretyakov highly appreciated Kramskoy’s talent. Due to similar life values, similar judgments and similar views on art conception and mission, they became close friends. In 1876 Kramskoy lived in Tretyakov’s house in Lavrushinsky lane while painting a portrait of Vera Nikolaevna Tretyakova - Pavel Tretyakov’s wife. And when Pavel Tretyakov himself got ill and had to stay at home, Kramskoy took advantage of the situation and created a portrait of the great art-collector - "Portrait of P.Tretyakov" (1876). Another portrait of the collector was painted by Ilya Repin in 1883.

Also in 1860-s Tretyakov became an enthusiastic supporter of a newly appeared Society for Circulating Art Exhibitions - the one that evolved into the school of the Itinerants (or “Peredvizhniki”) in Russian painting. Pavel Tretyakov attended all exhibitions of Peredvizhniki, encouraged them and supplied financially. Henceforth most of the pictures from those exhibitions were bought for the gallery. Sometimes Tretyakov would buy canvases right from the artists’ studios even before exhibitions. In 1870-s the pictures «Christ in the desert» by Kramskoy, «Pine trees forest» by I.Shishkin, «Rooks have arrived» by A.Savrasov, «Peter the Great interrogates his son Alexey Petrovich» by N.Ge  were acquired.

V.V.Vereshchagin, 1880

In 1880-s the collection had been considerably replenished. For a very high price - 92 000 roubles Tretyakov bought a series of Turkestan pictures and etudes by Vasily Vereschagin - the largest and the most expensive purchase for the gallery.  Also in that period many masterpieces were acquired: V.Surikov's «Morning of the Strelets’ Execution», «Menshikov in Berezov» and "Boyarynia Morozova"; I.Repin's «Religious procession in Kursk province», "Not expected" and «Tsar Ivan the Terrible and his son Ivan»; V.Vasnetsov's «After the battle of Igor Svjatoslavovich with Polovtsians», I.Shishkin’s «Morning in pine wood», I.Kramskoy’s «Inconsolable grief», N.Jaroshenko’s «Life everywhere», canvases of V.Polenov, I.Levitan, A.Vasnetsov, I.Ostrouhov.

Pavel Tretyakov used to place all pictures in his house in the Lavrushinsky lane, and though the house was big, he soon ran out of the space. Many times (in 1874, 1882, 1885 and 1892) the house underwent reconstruction: it was enlarged and new specially designed museum halls were attached. In 1881 Pavel Tretyakov decided to open the Gallery to public, but because of stealing pictures he had to close it in 1891.

By 1890-s Tretyakov became a very experienced collector. He would acquire pictures despite of the objections and even indignation of prominent artists. Thus in 1888 he bought V.Serov's «Girl insolated with sun», M.Nesterov’s "The Hermit" and "Young Bartholomew's Vision", I.Levitan’s «After rain. Pljos».

1892 became a significant year for the gallery: Pavel Tretyakov presented it to the city of Moscow.