He tried his hand at composition, advertising in the Wiener Zeitung of 11 January 1800 six minuets, six "Deutsche" and six contredanses in double editions, one for piano and one for two violins and cello.
For a period he acted as his brother's agent, but that ended after Ludwig discovered that Carl had attempted to publish some of his compositions under his - Ludwig's - name.
The relationship between the two brothers was always fraught. The brief period that they shared lodgings in the Theater an der Wien was marked by frequent rows between them.
Matters came to a head when Carl announced in 1806 his intention of marrying Johanna Reiss, daughter of a Viennese upholsterer. Ludwig considered her a totally unsuitable match, citing her reputation as a loose woman, a reputation compounded by the fact that she was already pregnant by Carl - a state of affairs that horrified Ludwig.
Despite Ludwig's opposition, Carl married Johanna on 25 May and their son Karl was born on 4 September.
The marriage - rather to Ludwig's gratification - was unhappy from the start. In 1811 Carl accused his wife of stealing money from him and reported her to the police; she was convicted and sentenced to one month's house arrest. On one occasion, during a fierce row, Carl stabbed Johanna through the hand with a table knife. A friend said she bore the scar as an old lady.
Having given up a career in music, Carl secured a lowly position as clerk in the Imperial Department of Finance. After some years he secured promotion and a small increase in salary.
Carl was dogged by ill-health and in 1813 he fell seriously ill with consumption - the disease that had killed the brothers' mother. On 12 April he wrote a declaration that in the event of his death he wished his brother Ludwig to undertake the guardianship of his son Karl, then six years of age.
His health improved, but a little over two years later the consumption took hold again and he fell terminally ill. His impending death - and the knowledge that he wished Ludwig to be guardian of Karl, in place of the boy's mother - caused Ludwig to mollify his feelings towards Carl. Ludwig was outraged when, a few weeks before his death, Carl's application for leave of absence from his office was refused.
The final day of Carl's life was fraught; he found himself manipulated first by his brother, then by his wife.
On 14 November 1815 Carl wrote as clause five of his will: 'Along with my wife I appoint my brother Ludwig van Beethoven co-guardian [of my son Karl].'
Ludwig persuaded Carl to cross out the words 'Along with my wife' and 'co-'. As he later wrote: 'I came upon [my brother's testament] by chance. If what I had seen was really to be the original text , then passages had to be stricken out. This I had my brother bring about since I did not wish to be bound up in this with such a bad woman in a matter of such importance as the education of the child.'
Later that day - in Ludwig's absence - Johanna, discovering what Carl had done, made him add a codicil to his will, properly witnessed, saying he had no desire that his son should be taken away from his mother, that he should always remain with his mother, and that she should exercise the guardianship of him along with Ludwig. He added - prophetically: 'God permit them to be harmonious for the sake of my child's welfare.'
His wish was not to be granted. Ludwig began a legal tussle with Johanna over the guardianship of Karl that was to last for more than four years, draining them both and severely affecting Karl's well-being.
Carl van Beethoven died on 15 November 1815 at the age of 41.
There is no contemporary image of Carl van Beethoven. The only description of him I can find is by Carl Czerny, Beethoven's pupil; its terseness and brevity speak volumes: 'Carl: small of stature, red-haired, ugly.'