The three-way trade had been planned since the beginning of the trade period but Melbourne and Geelong had to wait for Varcoe to agree to terms with Collingwood.
That could only happen once Dayne Beams had been traded to the Brisbane Lions.
Clark began to prepare tentatively for a comeback late in the season after retiring from Melbourne in 2014 following a diagnosis of clinical depression.
He looked set to join Collingwood but Geelong convinced him he could play an important role with the club and he joined the Cats.
Clark, 26, has played 97 games but managed just 15 in three seasons with Melbourne. He played 82 games with the Brisbane Lions. He has kicked 13 goals in seven games against the Cats.
Varcoe, 26, met with Collingwood coach Nathan Buckley while both were holidaying in Bali during the trade period and agreed to proceed with the potential trade.
The Geelong speedster played 138 games with the Cats and played in the club's 2009 and 2011 premiership teams. He attracted interest from West Coast but was always likely to stay in Victoria.
Melbourne met with Heritier Lumumba the day after he decided to part ways with Collingwood. He is expected to provide run out of defence.
Lumumba, 27, played 199 games with the Magpies including the 2010 premiership. Both parties agreed he needed a fresh start. Lumumba was All Australian in 2010 and finished fourth in Collingwood's best and fairest in 2014.
