In 1948, Coulter debated between running for mayor of Ottawa, or for a seat on the city's
Board of Control in the
1948 election. On October 4, he made his decision to run for the board. During the campaign, Coulter came out as fully in favour of the National Capital Plan, saying "[w]e can't bring industry here without annexing or taking in some additional territory". He stated that he wanted to be re-elected to council as he wanted "to be able to go before the government... and press for a larger grant than the present $300,000 for services rendered by the city". On election day, Coulter won 23,330 votes, more than any other candidate, and getting elected to the board. He topped the poll in
Elmdale,
Central,
Capital, Riverdale, and
Rideau Wards. Following the election, he was appointed to the board of directors of the
Central Canada Exhibition Association, to the National Capital Planning Committee, and to the Civic Superannuation Administration. As a controller, he was assigned the finance portfolio. He was also named "Acting Mayor" (essentially, the Deputy Mayor) when council passed a resolution naming whichever controller won the most votes in the previous election to the position. Following the annexations of parts of
Nepean Township and
Gloucester, Coulter, in his role as Controller of Finance, presented the city's highest budget in the history of the city up to that point. Coulter ran for re-election to the Board of Control in the
1950 municipal election. He ran for re-election in an attempt to "appeal to the voters on his record of 'service and integrity'", highlighting his work with the Capital Area Planning Board. During the campaign, he "looked favourably" on the idea of a five or 10 per cent tax on "occasional bingos" to help pay for indigent patients at hospitals,
Children's Aid and other causes. He also defended the board having to conduct some of its meeting behind closed doors, as they had to do with private matters involving staff. He supported reducing the size of council (which had expanded significantly due to recent annexations). He defended the city's recent annexations stating the problems "would adjust themselves and (in) a few years, everybody would be happy". He stated that the city's debenture indebtedness was reduced over the previous term, and he preached a fiscally conservative approach to more modern services, suggesting they only be acquired if they could be paid for. In terms of accomplishments by the board over the previous term, he cited "securing an increased grant from the federal government in lieu of taxes on government buildings". He believed this would increase over the following year. He also cited "substantial gains ... made in the purchases of the
OER assets for the
OTC. On election day, he was re-elected to the city's four-seat Board of Control, finishing in second place, with 31,071 votes, over 7,000 behind the first place finisher
Charlotte Whitton. Following the election, he was elected as president of the Ottawa
Shrine Club. He was also made first vice-president of the Central Canada Exhibition Association, and named as the board's representative to the new committee which was set up to administer the Darling report on civic wage scales. Following the death of Mayor
Grenville Goodwin in 1951, there was speculation that council would elect Coulter as the city's full-time mayor for the remainder of the 1951–52 term. However, he eventually announced he would not seek the city's top job, and backed interim-mayor
Charlotte Whitton instead. On October 15, Coulter was re-appointed as the city's Acting (Deputy) mayor, with Whitton's elevation to the mayoralty. In January 1952, Coulter was selected to be the president of the Central Canada Exhibition Association. That year, he also served as the chairman of the Ottawa Planning Area Board and the Civic Personnel and Superannuation Boards. ==1952 mayoral campaign==