Northall entered the service as a gentleman-cadet in the Royal Regiment of Artillery on 1 July 1741, and was promoted to the rank of lieutenant fireworker on 1 April 1742.

He served under Colonel Thomas Pattison with the Royal Artillery in Flanders in 1742, and was promoted to second lieutenant on 1 April 1744.

Then, after a more lengthened stay in Rome, he went to Loretto, Bologna, Venice, Mantua, Parma, and Modena, and returned to Leghorn, whence he sailed for Genoa.

[1] A posthumous account of his Italian tour was published in July 1766, entitled Travels through Italy; containing new and curious Observations on that Country.

… With the most authentic Account yet published of capital Pieces in Painting, Sculpture, and Architecture that are to be seen in Italy, &c., making up eight volumes.