The title Earl of Mornington was created in the Peerage of Ireland in 1760 for Garret Wellesley. On the death of the fifth earl it passed to the dukedom of Wellington, where it has remained. The subsidiary titles associated with this peerage are Viscount Wellesley (1760) and Baron Mornington (1746), both in the Peerage of Ireland.

The second earl, Richard Wellesley, was created Baron Wellesley in the Peerage of Great Britain in 1797 and Marquess Wellesley in the Peerage of Ireland in 1799, which titles became extinct at his death. The third earl had been created Baron Maryborough in the Peerage of Ireland in 1821. This title became extinct on the death of his grandson the fifth earl.

Barons Mornington (1746)

• Richard Wesley, 1st Baron Mornington (1690-1758)
• Garret Wesley, 2nd Baron Mornington (1735-1784), created Earl of Mornington

Earls of Mornington and Viscounts Wellesley (1760)

• Garret Wesley, 1st Earl of Mornington (1735-1784)
• Richard Wellesley, 2nd Earl of Mornington (1760-1842), created Marquess Wellesley
• William Wellesley-Pole, 3rd Earl of Mornington (1763-1845)
• William Pole-Tylney-Long-Wellesley, 4th Earl of Mornington (1788-1857)
• William Richard Arthur Pole-Tylney-Long-Wellesley, 5th Earl of Mornington (1813-1863)
• Arthur Richard Wellesley, 2nd Duke of Wellington (1807-1884)

for further succession, see Duke of Wellington

Barons Wellesley (1797) and Marquesses Wellesley (1799)

• Richard Wellesley, 1st Marquess Wellesley (1760-1842) (extinct)

Barons Maryborough (1821)

• William Wellesley-Pole, 1st Baron Maryborough (1763-1845), succeeded as 3rd Earl of Mornington in 1842
• William Pole-Tylney-Long-Wellesley, 4th Earl of Mornington, 2nd Baron Maryborough (1788-1857)
• William Richard Arthur Pole-Tylney-Long-Wellesley, 5th Earl of Mornington, 3rd Baron Maryborough (1813-1863)