The phrase "although he has established" is correct and usable in written English.
It can be used to introduce a contrast or exception regarding something that has been established by the subject.
Example: "Although he has established a successful business, he still struggles with work-life balance."
Alternatives: "even though he has set up" or "despite having created".
Although he had established himself as a top N.F.L. prospect after his junior season at Washington, he had not had a winning season or played in a bowl game.
Although he had established himself as an effective forechecker and defensive forward, Malhotra did not materialize into the offensive player the Rangers hoped he would be.
And although she has established herself as anything but a provincial writer, she is drawn back to coal country over and over again.
Although she had established herself as an actor on TV, on the Fringe and at the National itself, she has had to put that career aside.
"We believe that although they have established that money was paid and that official acts occurred," the lawyer, Michael K. Bachrach, said, "we do not believe the evidence supports one was for the other".
By February 1999, Siemens had given up trying to fix the locomotives, although they had established that the main fault lay in the generators.
Although Romney has established himself as favourite, there is still a route available to Gingrich if he can take big states such as Ohio, Georgia and Texas in March and April and sweep up the remaining southern states.
Although it has established a functioning democracy in a short period, other candidates in July's election challenged the results.
His fiction works are few and far between, although Perry has established a name for himself as a dab hand at espionage thrillers.
Although science has established that our love of sweet things is rooted in evolution, Krondl posits that "dessert is a purely cultural phenomenon".
