Mayor Martin J. Walsh, who has built a record-breaking campaign account since entering City Hall, has spent nearly $900,000 on a boutique fund-raising consulting firm that employs his longtime partner, accounting for more than half of the company’s political business since 2013.

The Walsh campaign’s payments to LB Strategies are growing in size and reached $13,500 a month last year. This is evidence, Walsh aides say, of the company’s expanding role in his political world. But the payments, and the ties to Walsh’s girlfriend, Lorrie Higgins, could create questionable political optics for the second-term mayor, analysts said.

The three-person shop, including owner Laurie Bosio, now oversees the operations of Walsh’s campaign office and its campaign mailings, in addition to scheduling, managing, and attending his fund-raisers, among other tasks, according to Megan Costello, a Walsh spokeswoman. Those duties, she said, go beyond those provided to LB Strategies’ other clients.