Aird, John (c.1760–1832), civil engineer, was born in Scotland; nothing is known of his parents or early life. In 1794 he began working for John Rennie (qv), one of the best-known engineers in Europe at the time, and remained with him and his son, Sir John Rennie (qv), for the remainder of his life. The early part of his career was spent in Scotland working as assistant engineer on several of Rennie's projects including the Crinan Canal (1794–1800), the East Dock, Leith (1801–6), and Greenock harbour (1807–8). When Rennie was appointed chief engineer of Howth harbour in 1809, he employed Aird as resident engineer and superintendent of works (1809–16), and thus Aird settled in Ireland, where he would remain until his death.
Work had initially begun on Howth harbour in 1807, but when the end of the pier collapsed, its chief engineer resigned. When Rennie took over, he proposed enlarging the works to two piers, east and west; and as resident engineer, Aird was given increasing responsibilities to ensure successful completion. The harbour was substantially finished by 1813, but Aird supervised its final stages until 1816. By this time, a group of harbour commissioners were deliberating a new harbour at Dunleary (Dún Laoghaire); Rennie was consulted for preliminary designs and, on their acceptance, was appointed chief engineer. With Aird again as resident engineer (1816–32), work began in 1816 on the east pier, but it soon became evident that it would not provide enough shelter from north-westerly gales, so an act of parliament was obtained (1820) that funded the construction of a west pier. During this period, Aird was also Rennie's resident engineer overseeing the construction of the Custom House Dock, Dublin (1815–24).
With the death of Rennie senior in 1821, John Rennie (later knighted) assumed the role of chief engineer of Dunleary harbour, and Thomas Telford was given responsibility for the Custom House Dock and Howth harbour. In all instances, Aird was retained as resident engineer because his experience and abilities provided well-needed continuity. He had great admiration and respect for his late mentor: while working (1820–26) on the west pier at Dunleary (renamed ‘Kingstown’, 1821), Aird admitted that Rennie's advice was sorely missed; and when he deviated slightly from the plans, he affirmed that the changes had had Rennie's approval. Aird worked as resident engineer in the construction of a road from Howth to Dublin (1823–4), and his distinguished reputation as a harbour engineer meant that his advice was sought when plans were considered for Balbriggan harbour (1818) and for one at Wexford (1822). Aird died at Kingstown in 1832, presumably in the summer months, since a new resident engineer of Kingstown harbour was appointed in August 1832.