After his return to Puerto Rico he worked as a general practitioner in various towns on the island, including San Juan.

During his administration San Juan's pedestrian and drainage infrastructure–and thus its general level of sanitation–was greatly improved; other modernizations resulted in the tearing down of a stretch of the city's ancient presidio walls.

In the midst of the 1898 U.S. invasion, Dr. Marxuach Echavarría assisted Dr. Coll y Toste (then serving as Vice-President of the Puerto Rican Red Cross) in treating the wounded during the fighting in San Juan.

The following year General George W. Davis, the American Military Governor of Puerto Rico, allowed municipal elections to be held for the first time since the U.S. invasion.

The Puerto Rico Republican Party enjoyed a sweeping victory in San Juan, as a result of which Manuel Egozcue Cintrón become Alcalde; Marxuach Echavarría, who was a political associate of Egozcue's, obtained a seat in the Municipal Council (Concejo Municipal).