Malo served as oral historian and court genealogist to the chief Kuakini, Queen Kaʻahumanu's brother, during the turbulent years when the old kapu system was abolished and Christianity reshaped Hawaiian society. In 1823, he moved to Lahaina on Maui and became a student of Reverend William Richards, learning to read and write in both English and Hawaiian. He converted to Christianity and took the baptismal name David — or Davida, as he spelled it following the open-syllable patterns of the Hawaiian language. Malo became a member of the first class at Lahainaluna School, the oldest educational institution west of the Rocky Mountains, and later served there as schoolmaster. His education did not erase his roots; it gave him tools to preserve them.

Beginning around 1835, Malo started recording notes on Hawaiian religion and cultural history alongside fellow students and instructor Sheldon Dibble at Lahainaluna. The class conducted systematic research into Hawaiian traditions, interviewing elders and compiling accounts that might otherwise have been lost. Their collaborative work was published in 1838 as Ka Mooolelo Hawaii. Malo also helped Samuel Kamakau establish the first Hawaiian Historical Society in 1841. He wrote a history of Kamehameha I, though that manuscript was lost. His magnum opus, Ka Moʻolelo Hawaiʻi, grew over decades. A second Hawaiian edition appeared in 1858 with additional stories. Nathaniel Bright Emerson translated it into English in 1898, and it has remained in print across multiple editions since. In 2017, an anonymous unfinished translation was discovered in the Bishop Museum archives, leading to a new bilingual edition published in 2020.

Malo's contributions extended well beyond scholarship. In 1841, he was elected as representative from Maui to the first House of Representatives of the Hawaiian Kingdom, making him one of the earliest Native Hawaiian legislators. He worked alongside Reverend Richards to translate the Book of Matthew into Hawaiian, serving as Richards's language teacher in the process. In 1852, he supervised the construction of Kilolani Church on Maui, whose ruins now stand on the grounds of Trinity by-the-Sea Episcopal Church near modern Kihei. That same year, he was ordained as a Christian minister at Kēōkea, Maui. He settled in the seaside village of Kalepolepo on south Maui, where he remained until his death on October 25, 1853.

Malo was buried above Lahainaluna School, on the hillside overlooking the institution where he had first learned to write. The school named its boys' dormitory after him and holds an annual celebration of his life each April. His legacy is the paradox of a man who embraced the new while mourning the old — who used the tools of the missionaries to preserve the very culture those missionaries were displacing. Ka Moʻolelo Hawaiʻi remains one of the most important primary sources on pre-contact Hawaiian life, a book written by someone who had lived within those traditions before they were transformed. His grief chant for Kaʻahumanu, his political service, his church-building, and above all his writing — these were the acts of a man determined that his people's story would not be forgotten.