Evangelist, administrator. He began preaching for the non-Sabbatarian Adventists in New England in 1853, and later the same year began to observe the Sabbath. In 1850, he married Mary How, who in 1869 assisted in organizing the first Vigilant Missionary Society. After doing self-supporting work in New England, in 1870 he was ordained and became president of the New England Conference (1870-1876, 1877-1887). In 1870 he organized the first conference Tract and Missionary Society and subsequently organized similar societies in various parts of the Eastern United States. He was president of the California Conference (1879-1887) and also of the Maine Conference (1884-1886) during that period, and part of that time was out of the country.
In 1885 he was in charge of a group that was sent to open denominational work in Australia. His preaching in New Zealand was climaxed by the forming of the first group of Seventh-day Adventists in that country. In 1887 with three Bible instructors he began SDA work in London, England, and organized a church there. He made a world tour in behalf of missionary work in 1889-1890, visiting Western Europe, Southern Africa, India, China, Japan, and Australia. In 1918, some 28 years later, in a report to the General Conference, he related that on that world tour he baptized one individual in China and another in Japan, the first in these countries (see Review and Herald 99:17, Dec. 14, 1922). No other reports of these baptisms are extant, nor do later historians on SDA denominational history mention them. He was again president of the California Conference from 1891 to 1894. His first wife died in January of that year. Again in Australia (1896-1899), he engaged in evangelistic work and taught Bible at the Avondale school. While there he married Hetty Hurd in February 1897. Another of Haskell’s “firsts” was the organization of the first African-American SDA Church in New York City (1902). After this, he conducted a series of Bible training schools and evangelistic series in Tennessee and California, and once again served as president of the California Conference (1908-1911).
He led in temperance work in Maine (1911), began printing books for the blind (1912), and assisted in the development of the White Memorial Hospital (1916). Until near the time of his death he attended institutes and camp meetings, and promoted the general work of the denomination. His written works include The Story of Daniel the Prophet, The Story of the Seer at Patmos, and The Cross and Its Shadow.