Sewall Mason Osgood was born in Henderson, New York, on March 2, 1807. He learned the printing trade through an apprenticeship in Watertown, New York, from 1822-1827 and then continued work as a printer and publisher in Utica, Cortland, and Watertown until 1833. In March 1834, the ABMU appointed him and his wife Elhira Brown Osgood to be missionary printers in Burma. On July 3, 1834, the Osgoods departed Boston on a ship named the Cashmere. Onboard with the Osgoods were two veteran missionaries, the Wades, and two Karen Christians (Moung Shway Moung and Ko Chet-thing). Three other new missionary families and one single woman were also on board: Hosea and Teresa Patten Howard, Justus and Calista Vinton, G.S., Sarah D. Comstock, and Ann P. Gardner. On December 8, 1834, they arrived in Amherst, Burma. Many of these families would make everlasting marks for the extension of God's Kingdom in Burma.

Osgood went to work right away in assisting Mr. Hancock at the printing press. In early 1835, while Mr. Hancock left for Serampore, India, to obtain a new font type, Osgood headed the printing of the Burmese Old Testament's first volume.

Osgood also assisted in starting the first Sabbath school for the Burman church in Moulmein. Early in his missionary service, he pastored the English church as Moulmein had a large English force stationed alongside some English businesses. Some who attended these English worship services included foreigners from India and other regions. Osgood took on this role before his ordination, which Adoniram Judson later officiated in May 1836.

While heavily involved in the printing press work, Osgood also led many evangelistic efforts in distributing them. In December 1836, he assisted Miss Macomber, a single ABMU woman missionary, set up a new outpost among the Pwo Karen in Dong-Yahn. Osgood would later return to Dong-Yahn and help with the baptism of many of these new converts. Not to be outdone by her husband; by 1836, Mrs. Elhira Osgood was managing two girls' schools with a total attendance of 19 students. Unfortunately, her health soon deteriorated from tuberculosis, and she died in Moulmein on October 5, 1837.

Many missionaries would leave the field facing such difficulties, yet, Osgood continued in his missionary pastor and printing work. On July 19, 1838, he remarried Sarah M. W. Thomas, whose missionary husband in the Assam Mission field had died in July 1837. Perhaps, the high mark in Osgood's missionary service was in his being the printer in charge of producing the first edition of Judson's complete Bible translation. Due to poor health, in April 1846, Osgood and his family retired from the mission field and arrived back in New York on  November 22,  1846.

In 1839, Osgood's second wife, Sarah, passed away in Wyoming, New York. Osgood showed a remarkable ability not only to be one sent in the cause of God's mission but to become a sender as well. After returning to the USA, he became a collecting agent for the ABMU. He also served as the ABMU District Secretary in the Northwest until his death on July 9, 1875. It was written of him: "The annals of our missionary history have not recorded the decease of a more devoted missionary, a more earnest and effective home worker, a truer man, and a saintlier Christian, than Sewall M. Osgood.”