In a book called Intellectuals and Society, A Study of Teachers in India
by Kameshwar Choudhary (2004), there is a more thorough research about the origins of the term:
The term ‘intellectual’... came to the English language partly through French in which it is Intellectuel, the word used for the first time in French in 1265 as a noun signifying one who is concerned with knowledge or
understanding.
According to The Oxford English Dictionary, the term intellectual signifies
a person possessing or supposed to possess superior powers of intellect.
It cites a number of examples of former use of the term. In 1652, for instance, Benlowes talked of
First race of Intellectuals.
In 1813, Byron said,
Canning is to be here, Frere and Sharpe, — perhaps Gifford... I wish I may be well enough to listen to these intellectuals.
In 1884, A.A. Watts referred to
The silent person who astonished Coleridge at a dinner of intellectuals.
On 30 November 1898 the Daily News reported,
Proceeding to refer to the so-called intellectuals of Constantinople,
who were engaged in discussion while the Turks were taking possession of the city.
On 19 December 1903, the Saturday Review
stated,
We are compelled to rank higher the mind of the average
young man of fashion than the mind of the average “intellectual”
_ at those literary tea-parties.
On 12 August 1960, the Times Literary Supplement mentioned,
The English have a great respect for brute facts; and the intellectual in politics often looks to them like a man busily engaged in brushing unpleasant facts under the carpet.
The same author then goes on to quote Raymond Williams, the Welsh writer:
Raymond Williams holds that the word ‘intellectual’ has been
an ordinary objective, from the fourteenth century, for ‘intelligence’
in its most general sense. However, it became a noun to signify the
faculties or processes of ‘intelligence’. According to him, the use of the word ‘intellectual’ as a noun to refer to a particular kind of
person or a person doing a particular kind of work dates effectively
from the first third of the nineteenth century though it had some
isolated earlier instances. Moreover, he notes the application of its
plural ‘intellectuals’ from the first third of the nineteenth century
to indicate ‘a category of persons,’ often unfavourably.
So Wikipedia's article does speak the truth, but probably could have provided more details and background for the evolution of the word.