Rynne, Michael Andrew Lysaght (1899–1981), civil servant and diplomat, was born 12 September 1899 in Hampshire, England, the first son of wealthy Irish parents Dr Michael Rynne and Mary Rynne (née O'Mara). The family moved to Limerick in 1907 on the death of his father. His siblings included Mary Rynne, who became an Abbey Theatre playwright, and Stephen Rynne (qv), farmer, writer, and broadcaster. He was educated at Crescent College, Limerick; Our Lady's Bower, Athlone; Clongowes Wood College; UCD; and the King's Inns, Dublin. He graduated BA (1920) from the NUI with first-class honours, and served as president of the UCD Students’ Representative Council (1920–21). In 1921 he sat his finals at King's Inns, but was not called to the bar for another four years.
From 1917 to 1923 he served in the Irish Volunteers, the IRA, and the national army. While a student in Dublin in 1917 he joined the Volunteers, quickly becoming a captain in C Coy, 3rd Bn, Dublin Brigade, and saw active service during the war of independence. He was involved in the events of Bloody Sunday, and as a captain at GHQ (where he earned the Service Medal with bar) was a close associate of Michael Collins (qv). During the summer of 1921 Rynne was in charge of the Blessington (Co. Wicklow) flying column, and served as ADC to Gen. Richard Mulcahy (qv). He was with his grandfather Stephen O'Mara (qv), Éamon de Valera (qv), and Cathal Brugha (qv) in Limerick when news of the signature of the Anglo–Irish treaty (December 1921) reached them. Shortly after the treaty was signed, he was appointed officer in charge of the military training camp at Dunboyne, Co. Meath. His success in this role came to the attention of Collins, who appointed him to set up an officers’ training school at the Curragh, Co. Kildare. However, the outbreak of civil war in June 1922 prevented the initiation of such a programme for a number of years.
At the end of the civil war (1923) Rynne resigned from the army to resume his legal studies. In 1929 he was awarded a Doctor Juris degree (magna cum laude) from the University of Munich for his thesis ‘Volkerrechtliche Stellung Irlands’, which prophesied, among other things, the return of the treaty ports to Ireland, and also envisaged Irish neutrality in the event of another major war. He also studied international law at the University of Paris; l'Institut des Hautes Études Internationales, Paris; the University of Berlin; the Academy of International Law, the Hague; and the University of Geneva.
Rynne returned to Ireland in 1930 and took up employment in O'Mara's bacon company of Limerick. He also spent a short time working in a bacon shop in Dublin before joining the Department of External Affairs in 1932 as an assistant legal adviser, and in 1936 became legal adviser to the department in succession to John Hearne (qv). As a member of the department's legal section alongside Hearne, he played a prominent role in advising de Valera on the means by which the 1921 treaty settlement could be dismantled. As head of the department's League of Nations section (1936–40), he was one of a small, closely knit set of advisers to de Valera on Ireland's relationship with the League of Nations, and accompanied de Valera on numerous visits to the League's assembly. Perhaps their most important journey was to attend the session convened to consider whether Haile Selassie, emperor of Abyssinia (recently conquered by Italy), could address the assembly. The League's decision was of great importance for other small states, and this was the basis of Ireland's position at the reconvened gathering. Rynne's advice to de Valera in 1937 not to attend that year's assembly, on the grounds that the agenda was not important enough, indicated a growing awareness that the League was irrelevant when the interests of the big powers were at stake.
After the second world war ended (1945) Rynne took part in delegations to Europe and the USA to establish Ireland's position in a rapidly changing world. By default he found himself dealing with matters concerning the newly founded United Nations, as no new appointment had been made for the purpose. Rynne viewed the UN as a more menacing vehicle than the extinct League of Nations; he feared that it could threaten Ireland's sovereignty, and his concerns centred principally on chapter seven of the UN charter, which he believed could allow the swallowing up of small states and neutral countries. He also advised on the recognition of the state of Israel during the period 1949–50; his views tended towards recognition de jure, although his political masters settled only for recognition de facto.
In 1950, after fourteen years as legal adviser, Rynne was appointed assistant secretary in charge of the Political, International Organisations, and Information sections of the department. In 1955 he was appointed ambassador to Spain, receiving the honour of Caballero de la Gran Cruz de Isabel la Católica from the Spanish government. During this time he informed his fellow ambassadors from other countries on the Irish government's line on such matters as the 1956 Suez crisis and the West Irian (West New Guinea) controversy. He retired from the civil service in 1961 and moved back to Ireland to live in Dundrum, Co. Dublin. Rynne also wrote poems, short stories, and radio plays under the pen name ‘Andrew Lysaght’, and in 1940 published two marching songs, Whistling on the road and Marching song of the four provinces. He died 8 February 1981 in a Dublin hospital.
He married (September 1931), in Paris, Nathalie Fournier; they had five sons – including Etienne Rynne, later professor of archaeology at UCG – and one daughter.