Although the united colony did not join the Canadian confederation when it was effected in 1867, the worrisome economic and strategic situation soon made such an arrangement attractive.

During the first provincial general election that October, McCreight won a seat for Victoria City in the legislature, and Sir Joseph Trutch, the Lieutenant Governor, chose him to be British Columbia's first premier.

His colleague, Henry Pering Pellew Crease, described the Premier as "bad tempered and queer...by fits & turns extremely credulous & extremely suspicious...excessively obstinate in the wrong places...close and reserved in his daily life...[and] utterly ignorant of politics".

His inability to form alliances and mollify the sometimes narrow and sectional interests of MLAs led to a loss of support, however, and in 1872, he resigned after losing a motion of no confidence following the Speech from the Throne.

He served as the first Treasurer (chief elected officer) of the incorporated Law Society of British Columbia from 1874 to 1880.