Frederick John William Lambart, 8th Earl of the County of Cavan was born on 30 December 1815 at his parent's home of Ower Cottage, Fawley, Hampshire, England. He was the son of George Frederick Augustus Lambart, Viscount Kilcoursie and Sarah Coppin.
His father, while with the Coldstream Guards, was severely wounded during the Peninsular War in the battle of Talavera and remained lame for the rest of his life until his death in 1828 at the age of 39. Frederick was left an orphan. He was sent to Eton from 1829 until 1833, where he was known, without his title, simply as Lambart. The Rev. Dr. Hawtrey was the then-headmaster and gave encouraging influence, which helped him succeed in his education.
At age 17, he was placed in the 7th Dragoon Guards, joining the regiment in Cork under Colonel Clarke. His service was at the time of one of the manifestations of the Irish rebellion. Martial law was proclaimed and the young officer was obliged to perform sad duties not according to his taste. In 1835, his quarters were changed from Carlow to Dublin. In the autumn of 1836 he was posted to Walsall, Staffordshire.
He married Caroline Augusta Littleton, daughter of Edward John Littleton, 1st Baron Hatherton, and Hyacinthe Mary Wellesley, on 24 July 1838 at St George's Church, Hanover Square, London. It was about this time, after the death of his grandfather, that he succeeded to the title and impaired estates. They remained married for 49 years and 5 months, and had five children:
After 1839 they went to Frankfurt am Main, then Bad Ems, followed by two years in Munich. It was here that his deeper biblical studies began. Upon securing a Bible in Dublin in 1835, religion began to play a part in his life. After 1844 he was, until his death, a member of the Open Plymouth Brethren. In 1846 Cavan went to Torquay and played a part in the formation of the Evangelical Alliance with Sir Culling Eardley. Among his special interests was biblical prophecy. He often preached on Christ's expected second advent. In 1866 Lord Cavan invited to come to Weston-super-Mare for evangelistic meetings. Dr. Friedrich Wilhelm Baedeker, cousin of Karl Baedeker, the famous travel guides editor, attended one of these meetings and experienced a religious conversion.