The building was designed by the renowned architect Charles Bulfinch of Boston, and in its original form resembles his Massachusetts State House.

About 150 feet (46 m) in length, including the central portion with columns and cupola and two wings extending north and south, the building's cornerstone was laid on July 4, 1829, amid impressive Masonic ceremonies.

In 1890–1891, a large three-story wing was added to the rear of the building to accommodate the State Library and to provide more office space for departments.

While the noble Bulfinch front was preserved, the length of the building was doubled to 300 feet (91 m) by extending the north and south wings.

A gilt copper statue of Minerva, the draped female figure of Wisdom, by William Clark Noble of Gardiner, surmounted the dome.

The governor's office is located in renovated space on the second floor at the rear of the central portion of the Capitol along with the Hall of Flags and the law library.

[5] The Maine Legislature's Legislative Council authorized the replacement of the copper sheath of the dome, which was long past its intended 75-year lifespan when it was installed in 1909–1910.

Democratic Assistant Senate Majority Leader Anne Haskell has suggested that at least some of the copper could be sold or auctioned to Mainers who might want a memento of the building, such as former state workers or legislators.

She also suggested some sort of contest could be held among artists for using the copper, perhaps as part of the State's "one percent for art" program.

It is conservatively expected that the portion sold to artists will bring approximately $12,250 to the State, while the making of souvenirs will cost about $3,600.