Born in Colwyn Bay, Conwy, North Wales, Sidlow played for Llandudno, Colwyn Bay and Wolverhampton Wanderers. Signed by Wolves in 1937 by the great Major Frank Buckley Sidlow was the first choice Wolves keeper both before the war. The rise of England great Bert Williams at Wolves after the war limited his chances, this included a notable international match between England and Wales at Ninian Park where Wolves supplied both the England Keeper and Welsh keeper. With Wolves having two international keepers this led to Sidlow being surplus to requirements, but a recognised international, Liverpool manager George Kay signed him for a then record £4000 in February 1946. Sidlow made his debut for Liverpool on 31 August 1946 in a league match at Bramall Lane, and kept his first clean sheet for the club, with Len Carney scoring a late goal for the Reds in the 90th minute. Sidlow's career was curtailed because of the Second World War which began when he was approaching his 24th birthday, having taken away the best years of his career he was almost 31 when he signed for the Reds. Sidlow with Charlie Ashcroft and Ray Minshull were the goalkeepers vying for the number one jersey at Anfield for the 1946/47 season; the first competitive season following the war. Even with the competition, Sidlow was given the position, which he held for 34 of the 42 games in a season that saw Liverpool win their first championship for 24 years. Much of which is owed to Sidlow as the final game of the season was a must win for the Reds. Sidlow's former employers Wolves needed just a point to win the title and Liverpool had to face them at Molineux. the Reds were a point back on their hosts and, needed a victory to win the league title. After a comprehensive 5–0 win at Anfield, Wolves were favourites to win the game and take the title, but goals from Jack Balmer and Albert Stubbins, plus Sidlow and the backline keeping Wolves down to one meant the Championship trophy would be heading to Merseyside. Sidlow tasted disappointment with the Reds too when they reached their first Wembley final in 1950, Arsenal where the opposition who took the FA Cup back to Highbury after a 2–0 win. Sidlow's Liverpool days were drawn to a close during the 1950/51 after he originally begun the season as first choice. Charlie Ahcroft and Russell Crossley took over for four games before Sidlow came back in to play his last match for the club, Anfield was the place and Newcastle United were the visitors. Things didn't go well for Sidlow and the Reds as The Magpies went back to St James' Park with the points after a 4–2 win. Crossley came back in to the side and Cyril retired in the August 1952, upon retirement from the top level, he went on to play for New Brighton. Cyril earned seven caps for Wales during his career.
Memorial
After his death his daughter sponsored a local award in Perton and Codsall, where her father lived until his death, to recognise local players achievements.
