With a passion for Georgian architecture,[1] Marshall is credited with building Perth's "new town" to the north and south of the city centre.

[9] He served alongside Thomas Black, who was shortly to become lord provost of Perth, and who died in office in the summer of 1798.

[7] Marshall co-wrote The History of Perth: From the Earliest Period to the Present Time, with information added by Henry Adamson.

[15] The proceedings gave way to several Scots ballads, including "Rosey Anderson": There was an Assembly into Perth, and Rosey she was there, Lord Elgin danced with her that night, and did her heart ensnare, Lord Elgin danced with her that night, she walked home on his arm, Hay Marshall he came rushing in, in very great alarm.

[2] His remains were brought from his home, by his relatives and the Duke of Atholl, to the graveyard of the Church of the Friars Preachers of Blessed Virgin and Saint Dominic at Perth, known locally as Blackfriars.