Burnett's (pictured) departure will bring to an end 16 years at Neptune, with 14 of those spent as a fund manager, including 13 running the £331 million European Opportunities fund.
Burnett will leave at the end of the year to set up his own fund management company called Lightman Investment Management.
A Neptune spokesperson said: 'It is entirely understandable that this is the right moment in his career to pursue this entrepreneurial path. After many years of valued service to Neptune and our clients, we wish him all the best in this endeavour.'
Burnett became manager of the £331 million European Opportunities fund in May 2005. According to Citywire data, since then he has returned 231%, outpacing the FTSE World Europe ex-UK index, which returned 194% over the same period.
Burnett's strong long-term returns have been delivered despite the manager's value approach having remained out of favour during the bulk of his time at the helm of the fund.
He has meanwhile endured a difficult 2018, with his fund rooted to the bottom of the Investment Association's Europe excluding UK sector since the turn of the year, down 18%.
His backing of Italian banks has hurt returns this year, amid the turmoil for Italian markets as the country's government populist government has clashed with the EU over its budget.
Smith is the top performing Latin America focused equity fund manager over the last five years. Over the period he returned 24.1% compared to a sector average of 2.6%.
In May this year he also took on management of Neptune India following the departure of Kunal Desai, who joined Mobius Capital Partners.
The Neptune spokesperson said: 'Tom has developed a highly replicable multi-country investment process over the past seven years in Latin America, which has enabled him to achieve a phenomenal combination of alpha generation and drawdown management and earned him numerous top ratings across the industry.
'Taking on Europe will give Tom the chance to apply this process on behalf of our clients in a mainstream sector and realise his potential as one of Neptune’s next household names.'