Walcott has agreed a new deal believed to last three-and-a-half years, pushing his wages close to £100,000 and ending speculation that another influential player would leave the Emirates Stadium.
The 23-year-old, who led Arsenal's fightback in Sunday's 2-1 defeat at Chelsea with a clinical finish, admits it was difficult to concentrate while his future remained in doubt.
"For the last three games before Chelsea the contract was sort of done, but it was on my mind and had been for a long time because it was so close," Walcott told Arsenal Player. "It is difficult to play and block out that side of it, but I tried to do the best I could and hopefully everyone was happy with what I did.
"I always wanted to stay and I am happy that myself and the club have come to an agreement. There has been so much speculation and I am very pleased my future is sorted. It is all about the present now."
The loss at Stamford Bridge has left Arsenal seven points adrift of the top four and a place in next season's Champions League.
It is a dire situation that has transformed Wednesday's home match with West Ham into a must-win encounter as they attempt to claw back some of the ground lost on fourth-placed Tottenham.
"There are a lot of teams that have got stronger this year, so we need to step on the gas. We don't want to be playing catch-up. We want to get points on the board," Walcott said. "We have a tough game at home against West Ham so we need to be ready. It is a massive game, we have home support and we need to start clocking up points there.
"We have been hot and cold at home of late so we must be very positive and if we show the commitment that we did in the second half against Chelsea we should be fine. We need to show that character to win from the start, not when we concede a goal."