He then won the 1875 Quebec election, but was removed from office on March 8, 1878 in a conflict with Lieutenant Governor Luc Letellier de Saint-Just.
Letellier de Saint-Just refused to approve legislation that had been passed by both houses of the Quebec legislature that would have forced municipalities to pay for railway construction.
Mercier was later cleared.
After Conservative leader Louis-Olivier Taillon had lost the 1890 election and his own seat, Jean Blanchet had taken over as Leader of the Opposition to the Mercier government.
Blanchet, however, had resigned on September 19, 1891, to accept an appointment as a judge.
The Lieutenant Governor therefore needed a Conservative to fill the post of premier, and turned to Boucher de Boucherville.
Boucher de Boucherville served for one year, but resigned when former Conservative premier Joseph-Adolphe Chapleau was appointed Lieutenant-Governor in December 1892.
Relations between the two may have been strained.
By 1915 the oldest legislator in North America, he died that year in Montreal at the Deaf and Dumb Institute, in whose work he was so interested that he lived there.