He was an amateur scientist and made some meteorological observations and wrote some papers. The astronomer François Arago took note of one of his papers written in 1852, which determined that the weather in his hometown was milder than that of Paris.
He then went to Paris in 1854 and worked at the Paris Observatory. There he assisted Urbain Le Verrier in creating a telegraphic meteorological network. He went to Brazil to observe the solar eclipse of September 7, 1858 and ended up staying there for a long time. He became a close acquaintance of the Brazilian Emperor Dom Pedro II, and became the director of the Imperial Observatory at Rio de Janeiro from January to July 1871 and again from 1874 to 1881.
Although the observatory had been founded in 1827, in reality it was occupied mostly with teaching students of military schools. Liais reorganized it to concentrate on research.
At the behest of the emperor, he made extensive exploration expeditions within Brazil and studied the plants of remote regions, sending some of them to France. He wrote a book entitled Climats, géologie, faune et géographie botanique du Brésil (Paris: Garnier Frères, 1872).
In 1878 a public dispute developed between him and Manoel Pereira Reis and his position at the observatory gradually became untenable. At the beginning of 1881 he resigned and returned to his hometown of Cherbourg.
He married a Dutch woman, Margaritha Trovwen, but they had no children. He bequeathed his property, located in a magnificent botanical park, to the city of Cherbourg. It is now known as the Emmanuel Liais Gardens.
A crater on Mars is named after him. In addition to the park named after him, there is also "Emmanuel Liais" street in Cherbourg.