Played for Caernarfon Rovers while working as a miner in two local collieries.

Moved to Cardiff City in 1942, signed by Cyril Spiers (ex-Spurs goalkeeper and then manager of the Bluebirds), with the inside right going on to play in war-time games for the Welsh club.  They were impressed by his ability and he signed professional in 1944.

Turned out in an international for Wales fifteen months after signing for Cardiff.

Scored 49 goals in 58 games up to the end of the war and in 1946-47, the club won the Third Division South championship with Rees leading the line.

When he left Cardiff City he had scored 33 goals in 101 league matches.

Signed for Tottenham in June 1949 for £14,000.

His debut was delayed because of a series of little niggling injuries, but scored on 22nd October 1949 against Southampton reserves, with his first team debut coming in the away game against Chesterfield in a 1-1 draw.  Scored his first goal in the next game four days later at White Hart Lane ... against Cardiff City !!

His first season ended with four goals in 12 reserve matches, 11 first team league appearances with three goals scored, along with two cup ties played.  Was part of the Second Division championship team in 1949-50.

Leyton Orient signed Billy in June 1950 for £14,500, where he stayed for six years and scored 66 goals in 198 games.

Left to join Headington United (who became Oxford United) of the Southern League in December 1955 and ended his time in the game at Kettering Town.

Back in his home town, Rees took up running a general store and worked in a pharmaceutical factory as a plant operator, while keeping pigeons in his spare time.

Lived in Llangeinor near Bridgend until his death in a Cardiff hospital on 25th July 1996 after a sudden illness.