John Bidwell's father was born in Massachusetts but moved to Canada just before the War of 1812. In Canada he did well in the lumber industry and married Abigail Benedict. Abraham and Abigail had seven children. Abraham was drafted into the British Army with the outbreak of war, but deserted soon after and fled to New York. He returned to Canada for his family and brought them to New York. Abigail died soon thereafter and Abraham, who was penniless, had to indenture all of his children. In 1816 he met and married Clarissa Griggs in Vermont and started a second family. Over the next two decades Abraham and Clarissa moved steadily westward. John Bidwell was Abraham and Clarissa's second child. He was born near Ripley, New York, on August 5, 1819. (Abraham and Clarissa eventually had a total of five children.)
By 1836 the family was living in Centerville just outside of Dayton, Ohio. The following year John left home to study at the Kingsville Academy in Ashtabula County. After one term at Kingsville he had learned enough to qualify as a rural schoolmaster. His first post was in Greenville, Ohio, but he soon tired of it and decided to move further west. In 1839 he moved to the Iowa Territory and took a 160 acre claim on newly opened public lands. In need of capital to improve his farmstead, he moved on to Weston, Missouri, where he taught school until the summer of 1840. On returning to his claim in Iowa he found that it was occupied by a squatter. Bidwell had never actually lived on the land and was under the legal age of 21 required for land ownership by single men. He had no legal recourse and had to abandon his claim to the squatter.
At this point in his life, Bidwell met Antoine Robiodoux, a French fur trader who had visited California. Robiodoux spoke so highly of California that Bidwell decided to move there even though it was at the time still a Mexican Territory.. His decision was reinforced by a farmer who was in correspondence with John Marsh, an early settler in California. Bidwell joined with others to form the Western Emigration Society which committed itself and all of its 500 members to rendezvous at Sapling Grove the following Spring. Subsequent news from California emphasized the dangers for Americans in California and most of the 500 original members of the society failed to show up at as promised. Bidwell and 60 others, including seven Jesuit priests, left on May 19, 1841, under the leadership of John Bartleson, and guided by Thomas "Broken Hand" Fitzpatrick, a famous fur trader.
After leaving western Missouri the Bartleson Party continued on through Kansas and Nebraska into Wyoming crossing the Rockies via South Pass and then proceeding to Soda Springs, Idaho. At Soda Springs, the wagon train broke into three groups. Father DeSmet and his six Jesuit priests, guided by a contingent of Flathead Indians, went on to Fort Hall on the Snake River. Another group of 22 souls, guided by Fitzpatrick, continued on toward Oregon. Bartleson, Bidwell, and the rest of the original party turned south and west toward the Great Salt Lake. After skirting the lake, the party headed out into the Great Basin and immediately began losing their livestock due to lack of feed and water. On September 16, 1841, the party was forced to abandon their wagons. Eight days later they finally reached the Mary's River (now known as the Humboldt River) and followed it until it disappeared into the Humboldt Sink.. From there they continued southwest till they reached the West Fork of the Walker River. On October 14 they were camped at the foot of the Sierra Nevada Mountains. It took a full two weeks for the party to struggle over the mountains but on October 30 they arrived in the San Joaquin Valley and on November 5 they reached John Marsh's rancho near San Francisco Bay.
The Bartleson wagon train was the first American party to cross the Sierras into California from the United States. (History frequently refers to it as the "Bidwell-Bartleson Party," but Bidwell was a young man of twenty and was not the party's leader.) California was still Mexican territory at the time and the group had to obtain passports from the Mexican government in order to remain in the territory. Their initial efforts were rebuffed by Major General Mariano Vallejo and fourteen of them were jailed for a few days until John Marsh vouched for them. Bidwell too was jailed when he attempted to obtain a passport but another American resident,Thomas Bowen, vouched for him and Vallejo provided the necessary papers. As soon as they received the necessary approvals, Bidwell and three others of the party left Marsh's rancho for New Helvetia where John Sutter welcomed him with open arms. Sutter had purchased Fort Ross from the Russians in 1841 and Bidwell was hired to take over supervision of its dismantlement from Robert Ridley. Bidwell remained in Fort Ross and Bodega Bay for fourteen months. In February 1843, he returned to Sutter's Fort. Over the next four years Bidwell assisted Sutter in a variety of roles including bookkeeper and manager.