He was among the first European architects employed by King Chulalongkorn (Rama V), and contributed extensively to Siam (now known as Thailand)'s architecture, especially the Neo-Classic, during the time of its modernization.

Grassi was born in Capodistria under the Austrian Empire (in present-day Koper, Slovenia).

He moved from Shanghai to Bangkok and in 1870 he joined Bonneville, a French timber merchant firm in Thailand.

Around 1875, Grassi Brothers & Co., his civil engineers company was established with his two brothers, Antonio and Giacomo Grassi, situated on the Chao Phraya River in Khlong San area opposite of the British Embassy then,[2] providing architectural and construction services.

In 1893, amid the conflict between Thailand and France, he sold his company, Grassi Brothers & Co. to Mr. Edward Bonnevillie and went back to his home town in Capodistria.