The nonviolence advocate Mahatma Gandhi was born in 1869.

Literal

Nonviolence-advocate [possessive-の] Mahatma-Gandhi [topic-は] 1869-year [in-に] was-born.

非暴力主義者 is a Sino-Japanese compound: 非 (non) + 暴力 (violence) + 主義者 (advocate/believer). Note the spelling マハトラ, likely a typo for マハトマ (Mahatma). A factual historical sentence.