 The order was founded in 1783 , a year after the grant of substantial autonomy to Ireland , as a means of rewarding ( or obtaining ) political support in the Irish Parliament . The Order of the Bath , founded in 1725 , was instituted for similar reasons . The statutes of the Order restricted membership to men who were both knights and gentlemen , the latter being defined as having three generations of " noblesse " ( i.e. ancestors bearing coats of arms ) on both their father 's and mother 's side . In practice , however , only Irish Peers ( and occasional foreign princes with tenuous or no Irish connections ) were ever appointed to the Order . The cross of St Patrick ( a red saltire on a white background ) was chosen as one of the symbols of the Order . A flag of this design was later incorporated into the Union Flag . Its association with St. Patrick or with Ireland prior to the foundation of the Order is unclear , however . One of the first knights was The 2nd Duke of Leinster , whose arms carry the same cross . 
