Horn, an electronics engineer and holder of a PhD in computer science, has also written extensively on technology and business innovation, and on privacy, including for The Irish Times.
[4][5][3] He continued study at Trinity, completing a PhD in Computing and Control Science and Technology in 1983,[2] the thesis for which, entitled Dada - the language and its implementation, was published in 1984.
[4] After completion of his PhD, he worked for a year as a consultant for Chaco, which later became part of Baltimore Technologies, as a contracted civil servant ("functionary") at the European Commission principal offices in Brussels, dealing with the ESPRIT programme.
[8] Eventually, in 1991, Horn, Sean Baker and Annrai O’Toole, all then academics in the Department of Computer Science at TCD, put in £1,000 each to found IONA Technologies.
The company, which did not raise angel or venture capital, but did have some IDA Ireland support, grew, and, after securing a 25% investment from Sun Microsystems in 1993,[9] was able to float on the NASDAQ,[10] achieving the fifth largest debut on that exchange to date.
[13] Horn invested in a search and advertising technology provider, Sophia (sold to Boxfish), Nomos Software and a data storage enterprise, Gridstore (later Hypergrid), among others.
[2] He served as a non-executive director on the boards two billing software companies, Sepro Telecom and LeCayla, and on a cloud-based dev-ops outfit, Cloudsmith, which he earlier co-founded.
[7] Horn was elected as president of Engineers Ireland[7] in 2008, and devised a detailed plan for his one-year term, reporting on progress against this during the year, attending or hosting 88 events.
[7] He commented about his shock and great disappointment at an abrupt announcement by Trinity College in late October 2021 that Science Gallery Dublin would close in early 2022, and called on Provist Linda Doyle, a former director of CTVR, to act to prevent the loss.
[17] In January 2013 Horn took on the chairmanship of Northern Ireland Science Park Connect, a program which aimed to support early-stage and "wantrepreneur" businesses, a role he held until 2016.
[24] In 1998, he bought an historic Georgian house, Askefield, the former rectory of the Church of Ireland in southern Shankill, then the home of journalist and politician Shane Ross, on 6 acres, for over £2 million,[11] and he and his wife moved their four young children there in 1999.