He served as the fourth Architect of the Capitol, and led the addition of the north and south wings and the central dome.

He retired in 1865, but financial difficulties forced him back to work in the 1870s, including a job as Chief Assistant to the Architect of Philadelphia City Hall.

[3] He worked as a bricklayer for his father during the construction of the Second Bank of the United States[4] and studied architecture in the office of William Strickland.

[5] He attended the School of Mechanic Arts at the Franklin Institute in Philadelphia and studied under John Haviland.

[7] In 1829, Walter was elected to the Franklin Institute; he would serve the museum in several roles, including as professor of architecture in 1841[4] and as chairman of the Board of Managers in 1846.

He visited England, Ireland, France, and Italy to study the architecture and construction of schools and other buildings and gather ideas for his work at the college.

Walter's fireproof cast-iron dome was authorized by Congress on March 3, 1855, and was nearly completed by December 2, 1863, when the Statue of Freedom was placed on top.

[12] He worked as Chief Assistant[5] to his friend and younger colleague John McArthur Jr., when he won the design competition for Philadelphia City Hall.

[16] Walter worked on over 400 projects over his career,[9] including: He married Mary Ann Elizabeth Hancocks in 1824.