St John will still remain active in the management of the small-cap fund as deputy manager.
He is stepping aside in order to concentrate on his other managerial responsibilities at Axa.
Rob Bailey, head of sales for Axa, described the appointment as a “natural progression for Henry”.
He adds: “Henry is taking over the smaller companies fund so that Chris can focus his attention on his mid-cap fund and his mandates in that space as well.
“He is going to stay involved in the management of the smaller companies fund as deputy fund manager.”
The £11.6m Axa Framlington UK Mid Cap fund has delivered an outperformance of 9.56% ahead of the FTSE 250 ex-Investment Trust index since launch in May 2011. Over one year, it has delivered growth of 8.13% while the index is down 1.43%.
The Axa Framlington UK Smaller Companies fund has delivered a 3.38% return over a one year period, against the -2.53% returned by the FTSE Small Cap ex-Investment Trust benchmark.