They would have extended their spending to around 50 million pounds if they had succeeded with a late bid for West Bromwich Albion striker Saido Berahino.
"I think we've done great business -- they're four very good signings," McClaren told a news conference on Tuesday.
"It's a statement of intent of what we want to do. We can go forward with a good squad...
"It's the ambition of the board and the club. We talked about it in the summer and we've carried it on in this window."
McClaren added that the bid for West Brom's unsettled forward Berahino showed the extent of their ambition.
"To make a huge bid like that for Saido shows the ambition we've got. He would have been a bonus but we're happy," the former England manager said.
Newcastle's local and relegation rivals Sunderland were also active in the January window, spending 15 million pounds, but bottom club Aston Villa kept their powder dry with no new signings.
McClaren said that third-from-bottom Newcastle should welcome back defender Paul Dummett, who has been out since mid-January, for Wednesday's league trip to Everton, who are 12th in the table.
"Jack Colback is also very close. Massadio Haidara should be fit by the Stoke game (March 2)," McClaren said.
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Toby Davis)
