The so-called "cold cases" include ones dating back to the founding of the force in 1974.
Det Supt Simon Atkinson, from the Homicide and Major Inquiry team, said the money would be used to employ 35 new staff.
The funding comes from the office of the West Yorkshire Police and Crime Commissioner.
Det Supt Atkinson said: "One undetected murder is one too many.
"That is why the PCC has announced these extra resources to recruit staff to review all these cases and we are determined to do our best to get some answers, to find the people responsible and to bring them to justice."
He said major advances in forensic techniques could make a real difference in reviewing all 55 cases.
West Yorkshire's most well-known unsolved murder cases include the death of 13-year-old Lindsay Rimer, from Hebden Bridge, in 1995.
Her body was found in the Rochdale Canal five months after she disappeared.
Lindsay's sister, Kate Rimer, said: "We miss her so much and every memory of her is tainted because of what happened to her."
Police and Crime Commissioner Mark Burns-Williamson said: "There are still people out there, in our communities, enjoying their liberty, who are responsible for terrible crimes.
"They present a real threat of further harm and need bringing to justice."
Mr Burns-Williamson said the money had been found from spending reviews and would fund the team for 18 months.

The 33-year-old ended a six-year stay at Bundesliga side Schalke, where he scored 126 goals in 240 games.
Huntelaar netted 102 times between 2006 and 2009 in his first spell at Ajax, who lost in the Europa League final against Manchester United this season.
"It is no secret that Ajax are my club. I am very happy to be back here," said Huntelaar, who has 76 Netherlands caps.
The former Real Madrid and AC Milan front man added: "I won cups with Ajax but not the league title. The goal is to have that trophy at the end of the season, along with the rest of the team.
"I feel very fit and I'm already looking forward to the end of June when the preparation starts."
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Violet D'Mello entered the enclosure for a photo next to the cats at the Kragga Kamma Game Park in Port Elizabeth earlier this year.
She suffered injuries to her head, stomach and legs during the incident.
The authorities in South Africa have ruled the park was not negligent.
A party of visiting schoolboys and a cheetah in heat were said to have been factors in what happened.
Mrs D'Mello, 60, said she survived by "playing dead". She had been on holiday with her husband Archie at the time.

Moaza Al Matrooshi, aged 24, gave birth in London after doctors restored her fertility using frozen ovarian tissue removed when she was a young child.
An advanced form of IVF using a donor egg as well as the mother's egg and father's sperm has been approved by the UK's fertility regulator. It is to prevent children being born with deadly genetic diseases.
BBC Radio 5 live spoke to a father whose 13-year-old son was groomed online and sexually abused. He explains how difficult it was to spot there was a problem until it was too late. He is warning other parents to monitor carefully what their children get up to online, and to "accept it can happen".  The charity Barnardo's says 297 children out of the 702 it supported in the last six months had been groomed online.
The award winning children's novelist Sally Gardner believes we should. She told BBC Radio 4's Today programme she "thinks in pictures" and that "there isn't one way to decode language".
The cost of Christmas dinner is at a four year high, with an average dinner and drinks now coming in at £10.71 per person. We spoke to family food bloggers and chefs to find their tips for bringing down the price as low as possible.
What family and parenting issues would you like the BBC to cover? Join the conversation - find us on Facebook
Funding of £1.5m will be used to help West Yorkshire Police review 55 unsolved murders.
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Dutch striker Klaas-Jan Huntelaar has rejoined Eredivisie side Ajax after signing a one-year deal.
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A South African game reserve where an Aberdeen woman was attacked by a cheetah has been cleared of any wrongdoing.
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Here is another chance to catch up on five of the best family and parenting stories from this week.