The building society increased gross mortgage lending by 17% to £21.5 billion in the year to April 4, accounting for 15.1% of all UK residential mortgage lending.
During the year it provided loans to more than 42,000 first-time buyers, a 75% rise on last year and meaning that the society was responsible for almost one in five of all first-time buyer mortgages in the UK.
Announcing annual results, Nationwide also said a record 123,000 customers switched their main banking relationship to the society during one of the most successful in its 26-year history of offering current accounts.
Executive director Chris Rhodes said: "Dissatisfaction with the big banks is leading people to vote with their feet.
"We opened new current accounts at a rate of one thousand per day over the last year and many of these were people switching from another provider."
Nationwide's current account base rose to 5.2 million and its market share of main and package accounts is currently 5.7%, up from 5.1% in 2012.
While arrears rates for its retail customers were well below the industry average, the performance of its £20 billion portfolio of commercial property assets has impacted on short term profitability.
Nationwide blamed weak tenant demand and a resumption of declines in property values for an increase in the division's bad debt provision charge in the year to £493 million from £247 million a year earlier.
Chief executive Graham Beale said: "We are working with our borrowers over the medium term to keep them in business and to protect members' interests."