Measures included streamlining distribution, staff training and awareness campaigns, fuel alternative trials and supporting customers with green products and services.
Booker has also increased backhauling, replaced mechanical handling equipment and refurbished dock bays.
All its branches offer recycling of used cooking oil, which is then converted to biofuel for use in Booker lorries. In the first few months of the programme, Booker has helped its customers recycle 200,000 litres of used cooking oil.
Chief executive Charles Wilson said: "We are delighted to be the first wholesaler in the UK to gain the Carbon Trust Standard and we firmly believe we have a responsibility to lower carbon emissions and reduce our impact on the environment. We are looking forward to continuing to work closely with the Carbon Trust to further reduce our carbon footprint."
Carbon Trust chief executive Tom Delay said: "We congratulate Booker on achieving the Carbon Trust Standard and challenge other organisations to follow their example and prove that they too are taking tangible steps to fight climate change."