SYDNEY, AAP – Australian share market investors had their biggest day of gains in more than four weeks ahead of a US Federal Reserve decision on monetary policy.

The heavyweight share categories of materials and financials were best on Wednesday as every category rose bar technology.

AMP shares gained more than nine per cent after the company sold its stake in life insurer Resolution Life for $524 million.

Meanwhile, the US central bank is tipped to scale back its $US120 billion ($A161 billion) monthly bond-buying program when board members meet this week.

The benchmark S&P/ASX200 index closed higher by 68.4 points, or 0.93 per cent, to 7392.7.

The All Ordinaries closed up 66.4 points, or 0.87 per cent, to 7713.

The Australian dollar was buying 74.37 US cents at 1621 AEDT, lower from 74.90 cents at Tuesday’s close.