A Manhattan art dealer was iced out of a hefty commission after selling a $1 million Mary Cassatt painting to a fancy Fifth Avenue gallery, a new lawsuit claims.

Plaintiff Christine Keefe says in court papers that she brokered the sale of the pastel-on-paper “Sketch of Tony” to Adelson Galleries for the big bucks on behalf of owner Rosalie James of Florida, but the seller has yet to fork over her promised $100,000 commission.

In the lawsuit filed in the New York Supreme Court on Friday, Keefe claims that James — an acquaintance of more than 15 years — approached her in 2015 and asked for her professional help to offload two Cassatt paintings, which she inherited, among a number of other works.

In July 2016, James signed an agreement to pay Keefe’s 10 percent commission based on whatever the paintings finally sold for, the suit says.

Adelson Galleries at 730 Fifth Ave. took both Sketch of Tony (1914) and The Mandolin Player (1868) on consignment in 2018 and sold Sketch of Tony for $1 million some time later, the documents state.

Having completed her end of the bargain, Keefe asked James for her $100,000 bounty for the sale but says James froze her out and cut off all communication, according to the suit.

The art dealer is seeking damages and her full legal costs.

James did not return a phone message seeking comment.

Keefe’s lawyer didn’t respond to a phone message or e-mail.