John Mercer Johnson (October 1818 – November 8, 1868) was a Canadian lawyer and politician from the Province of New Brunswick, and a Father of Confederation.

He represented Northumberland in the Legislative Assembly of New Brunswick from 1850 to 1865, and again from 1866 to 1867, each time elected as a candidate aligned with the liberal movement.

In the first parliament for the country of Canada, Johnson was elected to represent Northumberland, serving in the role from 1867 to 1868 as a Liberal member.

[2] In 1846, he became the secretary of the Chatham Mechanics' institute and lectured on phrenology, a belief that bumps on the skull can predict mental traits.

[4] The assembly was non-partisan but Johnson was considered a liberal candidate and campaigned on implementing responsible government.

[4] Under the premiership of Charles Fisher, Johnson was appointed to the Executive Council of New Brunswick on October 31, 1854, and became the province's solicitor general.

[6] He was reelected in the election on June 27, 1856,[4] but was not reappointed to the council when a conservative government won the majority of seats in the New Brunswick assembly.

[1] In 1860 he was appointed as a judge for the Inferior Court of Common Pleas and became captain of the revived 1st Battalion, which became known as the Chatham Rifles.

[2] He was re-elected as the assembly's speaker on February 12, 1862, but resigned later that year when he was appointed to be the attorney general under the premiership of Tilley.

[15] His belief was that parliament reflected citizens' political opinions, instead of each parliamentarian just representing their constituencies,[16] and that referendums were not required to change the constitution of Canada or to enact new policies.

[1] On September 4, 1867, Johnson was elected as the first representative for Northumberland in the Canadian House of Commons as part of the Liberal Party of Canada.

Their children included Ada E. Johnson, a teacher and organist, Andrew H., a lawyer, and Edward, who ran a stationery business in Chatham.

[21] A plaque was placed in 1927 for Johnson's honour at St. Paul's Church in Chatham by the Imperial Order Daughters of the Empire.