The secondary school was previously known as Hounslow Manor School, which was judged 'good' by Ofsted inspectors when they last visited in 2011.
But the latest report, published on Friday (June 5), concluded the school, which is part of the London Academies Enterprise Trust (LAET) network supported by Mr Johnson, was now underperforming.
It was rated 'requires improvement', the second lowest of four possible grades, overall. Four out of five categories assessed, including teaching and achievement, were also judged 'requires improvement', with only pupils' behaviour deemed 'good'.
Inspectors, who visited in May, said disadvantaged and white British students were making less progress than other pupils in English and maths.
They also criticised "inconsistencies" in the quality of teaching and said sixth formers were not getting the necessary information, advice and guidance, leaving them lagging behind their peers nationally.
However, headteacher Anjali Sakhardande said the academy had achieved its best results last year and Ofsted's own 'data dashboard' showed most groups of students there are making better than average progress.
"The academy already has plans in place to make rapid progress and embark upon the good to outstanding journey," she added.
"There are also some queries about procedures followed during the inspection which have been raised by the academy."
Academies are state-funded independent schools, which are free from local authority control and don't have to follow the national curriculum.
When Hounslow Manor School converted to academy status two years ago, Ms Sakhardande said the move would help build on its existing success and "strengthen our rapid progress to outstanding".
Mr Johnson said when opening the academy that he wanted to work with employers to set up more work placements and training opportunities to improve students' career prospects.
Kingley Academy last August achieved its best ever GCSE results, with 50% of students securing five or more A*-Cs including English and maths - more than 10 percentage points up on 2013.
The school's A*-C pass rate at A-level was 70%, with the proportion of A*-B grades up 10 percentage points from the previous year.