The phrase "although he has maintained" is correct and usable in written English.
It can be used to introduce a contrast or exception regarding someone's ongoing actions or beliefs.
Example: "Although he has maintained a positive outlook, the challenges continue to mount."
Alternatives: "even though he has upheld" or "despite his continued assertion".
The Mayor Although he has maintained his distance, Mayor Bloomberg clearly has an interest in the outcome, both as a public official and as a private philanthropist.
He likes the size and collegiality of his conference, although he has maintained publicly that he would make a move if there is a "paradigm shift".
Winfield has annually drawn a list, although he has maintained that he has done it only to give the Yankees a sense of which clubs he might consider playing for.
Although he has maintained a high profile throughout most of his public life -- his current job places him first in line after the Mayor in the city's elected hierarchy -- and has held jobs that gave him influence on a range of issues, he has enjoyed little direct authority.
Sirhan testified that he had killed Kennedy "with 20 years of malice aforethought", although he has maintained since being convicted that he has no memory of the crime.
Kesha is trying to bring it back to what it believed in". On the Republican side, Cornyn is facing a field of seven challengers, although he has maintained a commanding lead in the polls.
Although for two years he has maintained that he would be a candidate this year, Mr. Rivera is now somewhat cautious.
Sharapova has not played since, although she has maintained a high profile at public appearances to promote her confectionery business.
Ruth Handler was indicted and later pleaded no contest in 1978 to a securities law violation, although she has maintained her innocence.
Mr. Margulies said Dr. Mitchell had never practiced psychology in Texas although through the years, he had maintained his license here and renewed it.
And although she had maintained that she did not send classified material and that she eventually turned over all her work-related email to the State Department as required by law, it turned out there were some 15,000 messages among those she'd ordered her staff to delete as personal that actually contained work-related material.
