Charles Darwin published his book On the Origin of Species on November 24, 1859, which was 23 years after he returned from his voayage to the Galápagos Islands. Darwin knew that his theory would be found controversial at the time, which is why he was hesitant to publish. At the time, scientists believed that species were fixed, which is the direct opposite of what Darwin's research suggested. Darwin was also afraid of the probable religious backlash that he would receive, fearing being declared a "heratic" with "blasphemous" ideas. 

Darwin received a letter from an English naturalist Alfred Wallace in 1858 where Wallace gave a summary on his theory, On the Tendency of Varieties to Depart Indefinitely from the Original Type. Darwin was surprised at the fact that Wallace wrote out what was essentially Darwin's theory. After the two met, Wallace encouraged Darwin to publish his findings with Wallace's as support because Darwin had signifigantly more research in favor of his theory. A little over a year later, Darwin published his theory. 

Only 1,250 copies of On the Origin of Species were printed, in anticipation of the public uproar that Darwin suspected would occur due to his theory. All the copies sold out in one day. Though many people, including some of Darwin's family and friends, were angry with his findings, many found Darwin's theory fascinating and agreed with him due to the amount of evidence he compiled. Darwin went on to publish many more books throughout the 1870s.

Sources: 

https://necsi.edu/darwins-later-life