Allen was admitted to the bar in 1825 and commenced practice in Brattleboro, Vermont. In 1830 he moved to Bangor, Maine and entered into practice with John Appleton, who would subsequently become Chief Justice of the Maine Supreme Court. Appleton would also marry Allen's sister Sarah in 1834. Allen was a member of Bangor's first City Council, from 1834, and from 1835 to 1840 was a member of the Maine House of Representatives, representing Bangor. He served as its Speaker in 1838. From 1841 until 1843, he served in the U.S. House of Representatives as a member of the Whig party, but his district was eliminated before the next election based on census data. He ran in the 1842 election against Hannibal Hamlin but was defeated. Following this loss, Allen ran for the Maine Legislature once more, serving one term before moving from Bangor to Boston in 1847 and being elected to the Massachusetts House of Representatives in 1849.
Kingdom of Hawaii
From 1850 to 1853, he was United States Consul in Honolulu, Hawaii under president Millard Fillmore. He realized the potential for the Hawaiian Islands to provide agricultural products to the growing number of people in the California Gold Rush and tried to negotiate a trade treaty but failed. When he was replaced by an appointment from the Democratic Party president Franklin Pierce in August 1853, he decided to stay due to the severe shortage of legal professionals, and became a citizen of the Kingdom of Hawaii. Within weeks he was appointed Minister of Finance for King Kamehameha III replacing Gerrit P. Judd, and from 1854 to 1856 served in the House of Nobles. He openly advocated annexation of the islands by the United States, and opposed French and British influence. However, when King Kamehameha IV came to the throne in 1855, the annexation idea was put on hold. During Kamehameha IV and Queen Emma's wedding in 1856, he offered his own wedding band to the king to allow the ceremony to continue. In June 1856, Allen sailed back to New England and remarried in Philadelphia. The newly married couple returned to Honolulu, where from June 1857 through February 1877, Allen was Chief Justice of the Kingdom of Hawaii Supreme Court. The Allens' first-born son, Frederick, was born ten days after Prince Albert Edward Kauikeaouli Kaleiopapa, and the two children became playmates. The prince died when he was only four years old.
Minister to the United States
From 1856 until his death in 1883, Allen served as Minister Plenipotentiary from the Kingdom of Hawaii to the United States. In August 1864, he served as Chancellor for the coronation of King Kamehameha V under the new 1864 Constitution of the Kingdom of Hawaii. In 1864, he tried again to negotiate a trade treaty. During the American Civil War sugar shipments from the American South were interrupted, increasing the demand from Hawaii. In 1867, he bought a sugarcaneplantation in an area called Princeville, Hawaii after the young Prince brought up with his son. He negotiated for the Reciprocity Treaty of 1875 which this time was signed by Ulysses S. Grant. The treaty removed tariffs but gave the U.S. the use of Pearl Harbor, which was not a popular concession with native Hawaiians. He left his son William Fessenden Allen from his first marriage in charge of the plantation, and went to Washington, D.C. to work out details of the trade agreement. He returned briefly to Hawaii, but his two children from his second marriage were back in the United States, so he resigned his supreme court post and went back to Washington in February 1877. The plantation did not live up to his hopes. By 1879 it was losing money, in debt with a mortgage, and needed a new manager. He wondered if it was doomed to a fate similar to the prince for which it was named. Finally the plantation paid dividends starting in 1882.
Ellen Fessenden Allen, who married George Tiffany. After his death, she married Henry Adams Patterson, and, thirdly, Charles Coffin Harris, her father's successor as Chief Justice and Chancellor.
William Fessenden Allen, who married Cordelia Church Bishop, cousin of banker Charles Reed Bishop. William also served as Collector-General of the port of Honolulu.
Elisha Hunt Allen Jr., who served as Hawaiian consul in New York and who married Julia Anne Herrick.
In June 1856, he sailed back to New England and married Mary Harrod Hobbs in Philadelphia on March 11, 1857. Mary was daughter of another former Maine legislator Frederick Hobbs. Together, they were the parents of two children, including:
He died from a heart attack at a New Year's Day reception for the Washington Diplomatic Corps given by president Chester Arthur at the White House on January 1, 1883, shortly before his 79th birthday. Allen is one of ten people known to have died inside the White House. He is interred in Mount Auburn Cemetery in Cambridge, Massachusetts.
